first of all, I did not say a lesbian emily would be bad, any non-stereotype LGBT characters are good, no doubt. I just hope it won't be that because it would be a bit disappointing after that announcement and not that progressive. and I used the word "effective" when i actually should have specified more "progressive", but to clear up the confusion I will gladly elaborate on that.
as others pointed out, a lesbian would be "the easy way out", it's not progressive because girl on girl action is not perceived as negative in our society, unlike man on man action. I use the stupid term "action" here because I want to specify that I am not talking about real relationships here but the "wow that's hot dude" mentality when two girls kiss at a club and the men are cheering. that's not a real homosexual relationship but sadly that's what most lesbian relationships are reduced to in games and other media because that way, and only that way it pleases the straight white male audience. if the lesbians are not sexualized porn stars they are ridiculed like gay men, so this is clearly not about including LGBT but to produce eye candy for the male straight audience. only in very rare cases is that done right, I want to point out the last of us dlc here.
but dishonored, and I absolutely love that game, I finished it three times in a row and it's my favorite new franchise of the last generation, is very stylized game. it has a victorian and burlesque character design, which I love, but I don't see a grounded lesbian relationship possible here.
and because of those reasons I would think a straight female player character with a male romance option would actually be far more progressive, because that is something that is surprisingly rare in videogames. female player characters are rare enough but a forced female character with a forced male relationship is next to non existent. while the opposite is happening in almost every story driven game. of course nathan drake hooks up with his female companion, it's completely natural. lara croft however does not find romance, her male companion remains just a friend. playing AC: Syndicate last year made me realize how rare that is, because there Evie Frye is actually pursuing a romantic interest, but she is only one of two main characters and the focus was much more on her brother in the latter half of the game and the romantic interest more or less disappeared.
and this is the main reason why I think a straight female would be far more progressive. as much as I want lesbian players to have an experience in games that suits them, I think there is a far bigger neglected audience that has not had their due, yet. the straight female audience, and I think it would be great to include them more, and not only in RPGs where all kinds of romantic relationships are possible anyway.