I should clarify that when I say there's no evidence she'd commit adultery, I thought the "yet" was implied, since this is a WIP.
Of course for at least the four main characters, there's going to some point at which she breaks and cheats on Liam, there'd be no point in the game otherwise.
And yeah, much of the fun at the moment (for me at least) is watching the two sides of Sophia war with each other. For the Ellie/Patricia route, because Sophia can't have sex with Liam on it, she's incredible horny. Ellie and Patricia offer harmless release from it that isn't adultery, but it's incest. But she's testing the boundaries, even got caught by Liam once, and she's got away with it. He even seemed fine with it.
From what I've seen of the Sam route if you take it, is that yeah, as you say, Sam fits Sophia's weakness of being a rock muso, combined with the teasing Sophia apparently does at every opportunity on the route, takes her back to her college days. Having sex with Sam wouldn't be incest, but it would be adultery.
I'm not aware of what attraction Sophia might have for Dylan. Sure, she loves him as a son, but attraction? Plus he has the double whammy of sex with him being adultery and incest. Personally I think he might be the last to have sex with Sophia just based on that, but we'll just have to wait and see. Oh, and with Dylan being the most popular character, L&P has the most by patrons possibly getting bored after the sex scene and stopping their subscriptions.