The way she's holding the Saber towards Luke in the end is definitely a sign of giving it to him. It's a question of whether she'll want to down the route of being trained. She definitely seems sure of herself at the end of it, when Leia tells her 'The force be with you' and she smiles.
Literally nobody said that. So what if she goes dark side? You wouldn't think that's interesting? It has nothing to do with her gender. If it was Finn in her position, I'd want him to go dark side as well.
Why? Why does going to the dark side suddenly make her or Finn more interesting than they already are? What are we gaining narratively from them going to the Dark Side? There are already plenty of Dark Side characters in the movie. Adding Rey or Finn to the mix will accomplish, what, exactly? The "oh shit, now he/she is a BAD GUY!" factor holds little interest in and of itself. Of course, a character going to the dark side could be handled well by competent writers, but the truth of the matter is that as a creator, you most certainly, 100% have to sit back and think of the message you are bringing across in your work. It's also 100% your discretion to go through with it anyway.
Rey is one of the few genuinely well handled female protagonists in film. She is smart, resourceful, funny, good natured, and honest. Little girls and grown women are flocking to her because she's a female in fiction that is actually getting to do the shit that the "big boys" have been doing for generations of film and television (and other media like novels). As a result, there is a lot of careful thought that has to go into how this character is handled. Because she's such a rarity, if she falls to the Dark Side, the message it's sending, even if it's unintentional, is that a woman, when given power, is unequipped to handle that power. The truth is that there is simply a different set of standards applied to women than men (and vice versa), and in the case of female protagonists, especially female protagonists in something as mainstream and culturally relevant as Star Wars, means way more to women fans of Star Wars than male fans, who have had, quite literally, 6 movies be about them being awesome and capable, and heroic, even if one of the 9 primary characters across the two trilogies fell to the Dark Side.
Having Rey, the first female character in a Star Wars movie to actually DO SHIT, fall to the Dark Side would be a grave misstep, and on a personal level, I don't think it would add to the story from a dramatic standpoint. When would you have her turn? In the second movie, and then what happens in the third? Does she have an equally abrupt change of heart (the wishy washy nature of women, right?/s), or does she continue to fall to the Dark Side, dying a villain's death, and thus cementing another failure of Luke Skywalker's teachings as a Jedi "Master?"
As I mentioned in a super long post above, you have to consider how the characters various story arcs play off of, and affect other character's story arcs. Look at Obi-Wan Kenobi. His primary arc is that he took Anakin Skywalker under his wing, and failed him. Anakin fell to the Dark Side, and was lost. The back end of Obi-Wan's arc is that he redeemed that failure by training Anakin's son, Luke, thus leading to Luke being able to do what Obi-Wan couldn't, and bring Anakin back to the light side of the force.
Luke's arc, as the new Obi-Wan figure, is that after redeeming his father, he started up an academy, but his nephew, of all people, fell to the Dark Side and wiped them out. Leia thought that Luke could help her son, and he failed her. He failed Han. He failed Ben Solo. Of all of the talk about how TFA "robbed" the trio of their happily ever after hinted at in Return of the Jedi, following up Luke's failure with Ben Solo with
another failure of teaching would be like kicking a puppy with a broken leg. It would be sloppy story-telling. Storytelling that was more concerned with having their "Oh shit" moment than considering how a "Dark Side Rey" arc would reflect on the other characters in the film, and their personal arcs. How much failure should Luke have to endure before he dies? It just doesn't make sense to me that they'd follow up Ben's fall to the Dark Side with Rey's fall to the Dark Side. Especially when, as set up by TFA, Kylo's arc trajectory does not look like that of one of redemption. He is going to fall even deeper into the Dark Side. The conflict he felt in TFA was extinguished when he killed his father. Yes, he was torn apart, and the immediate aftermath of that event was him getting bested by Rey, but now that his "test" is over, and he passed, he is ready to take the next step. To upgrade.
Rey's arc seems to be that of a gifted Force user coming to terms with her past, and finding a balance in herself. I feel like true "balance" in the Force, is one of accepting that there is both light and dark inside of you. Yin and Yang. The Jedi tried to purge all darkness. The Sith tried to purge all light. True balance and harmony is learning to become one with both aspects of your nature. Rey displayed both Light and Dark qualities throughout the movie, and especially in the end of the film. She is wearing neutral gray in the very last scene. Perhaps a visual metaphor for that potential balance of Light and Dark.
I don't doubt that she is going to be tempted by the Dark Side, but unlike the prequel trilogy Jedi and Sith, I think she is going to be one of the few Jedi that masters the light and dark sides of herself. That's what will make her arc different and interesting compared to Anakin and Luke's. And it will also be a moment of redemption and victory for Luke Skywalker as well, once he learns, through his new apprentice, that running from your Dark Side is just as damaging to your being as embracing it. It should be a very interesting, and different trilogy from the first two if that is the case. But no, I don't think that Rey going Dark Side would be interesting. It would be, to put it frankly, typical mishandling of strong women in fiction.
I have yet to hear a compelling explanation as to why Rey going full Dark Side, and Kylo going Light Side, would make a lick of sense beyond the "cool" factor. The subtext from a few people is that Rey goes bad because women can't control their emotions. Obviously, that's not why EVERYONE that thinks Rey should go Dark Side, but a lot of it seems to come from the uncomfortable feeling some people have about the fact that Rey is just so damn good and capable; a rarity in fiction. Like it's literally unbelievable that a
girl could be an excellent pilot, fighter, and Force User. These same arguments are often handwaved when the lens is focused on male characters like Luke and Anakin, who displayed just as much capability in similar scenarios as Rey. The only thing I can take from that line of argument is subconscious sexism. Not all men (or women), that have a problem with Rey do so because of sexism, but obviously, if it doesn't apply to you, there's no need to get offended by it when someone mentions it (there is already ample evidence out there that people have issues with both Finn and Rey because he is black, and she is a woman, respectively). I'm not going to shy away from mentioning sexist motivations concerning some people's dislike of Rey, or racist subtext and motivations for people's dislike of Finn, because they are uncomfortable to consider, even in something as fun an family friendly as Star Wars.
And as a black man, yeah, I'd actually be pretty annoyed if Finn was Force Sensitive, and fell to the Dark Side. Because, for me, it'd be just another example of the "Angry Black Man," who can't control his anger, and is bad. Women and minorities are in a lot of the same positions as far as positive, encouraging representation in the media. It's easy to shrug off that lack of representation when you are part of a privileged group that has diverse representation in media. A white drug dealer in a tv show, for example, is an anomaly. A black drug dealer in a tv show, is par for the course. A strong, capable, intelligent, multi-talented white guy in fiction, is a dime a dozen. A strong, capable, multi-talented black woman in fiction, is an anomaly. So yeah, women and minorities get really attached to any positive representation we get thrown our way in various media. And if that representation suddenly turns sour, it stings just all the more, because of the lack of so few alternative positive representation, especially on the level of Star Wars. Women and minorities are expected to get the same level of heroic inspiration from white males as they would a heroic woman, or a heroic minority (whether it be a minority male or female). But that's not really how psychology works, and the lack of role models that look like you is mentally and emotionally damaging, even on a sub-conscious level. It would suck really bad to have yet another female/minority fall into the same tropes and cliches and stereotypes they always fall into.
I've mentioned it before, but growing up, in school, I wasn't allowed to be Batman, Superman, The Flash, Green Lantern, or Spider-Man (five of my favorite heroes ever at the time), because I was black. I had to be the bad guy that my white friends (all playing, Batman, Superman, The Flash, etc) got to beat up. And I didn't even get to be a bad guy with powers (they were all white too: Lex Luthor, Joker, Sinestro, etc), I got to be the generic thug who was robbing the bank, and the JLA (with honorary inductee Spider-Man), got to foil. So yeah, when I learned of characters like John Stewart as Green Lantern, or learned of Luke Cage and Falcon, and Black Panther, and recently with Miles Morales becoming Spider-Man, you can't imagine how absolutely excited I was that I could finally join in on all of the superhero fun that my classmates were having now that there was a hero that I could actually be. Funny aside, but in my neighborhood, all of my friends were black, because it was a predominantly black neighborhood, and we all got to be Batman, Superman, Spider-Man, etc when I played with them, but I didn't see them as much as my classmates in school, who I spent the entire day playing with.
So, yeah, having the few well represented, developed, likable, and charming black and female protagonists in Star Wars go bad would be a lot more damaging and upsetting than many realize. I applaud Abrams and Kasdan for creating Rey and Finn, and handling them so excellently (the trick was writing them like any other character, regardless of gender and ethnicity).
Sorry for the long rant. My apologies.