It's not a good sign when the fans are already speculating that Snoke is Vader, after the movie made 900M. It's also not a good thing that all audiences witnessed before they left the theater was the main villain getting his ass whooped by two Jobbers, and a upper midcarder in Rey all in one movie.
You said it yourself; it's speculation. The movie has been released and people like to speculate about certain things in order to get a discussion going. It has
nothing to do with people wanting Vader to replace Kylo Ren.
Also, it's a trilogy, whereas we (the audience) acknowledges the fact that Ren is going to get tons of training for the next movie (Snoke said this to Hux in the end). Also, he could've killed Finn multiple times (he was knocked the fuck out but decided to do a 180). He also
couldn't kill Rey because he wasn't allowed to. During the part where he tells her
''You need a teacher'', he could've easily pushed her down the cliff - but Snoke wants her alive. You'd be silly not to understand that. Also, if you need more shit in the oven, here you go:
- Killed his father, resulting in even more of an emotional mess
- Clean shot on the waist by a bowcaster (metallic bolts). During the movie, they've pointed out (three times) that one of these shots instantly kills the person, including the stupid shit TR-8R.
- Right (main) fighting arm nailed with a lightsaber blow from Finn