IN terms of what I want to see as mentioned by kinglionheart there are a few things:
Online, you are right, there's a lot that could be done there. Hidden sex there would be the way to go, just different scenarios, in particular behind the back stuff. Lots of different costumes.
Real Life: Inoda vs Kirito outside of sex. I want Inoda to start to prove he's better boyfriend/future husband material than Kirito in various ways instead of just sexually. Really have more POV from Asuna's perspective as she realizes that she is falling for Inoda as a whole rather than just sex with him. Make it a very slow emotional descent to join the physical.
Oh, and more sexy times in the real world - dates, foreplay, kissing. Just because you've reached the sex stage once is no reason to not go back and do more things. This can tie into the above, with Asuna realizing she enjoys more just being with Inoda rather than just sex. And when it comes to sex, there's obviously the whole condom/pregnancy scare type stuff to play with.
Gameplay: I'd like to see some more branching scenarios. Maybe a Suspicion rating, where if you want you can guide Kirito to find out the truth over time, and see how he handles it from there. If Lisbeth and other characters are coming in, then maybe Kirito could find comfort with them, breaking up with Asuna?
Which leads into, to repeat, endings: These are the ways I would like to see the game end: One, Kirito finds out. Two, he doesn't, and Asuna stays with him, either because some part of her still loves him or just enjoys the guilt and thrill of cheating behind his back. Three, Asuna is pregnant and leaves him. Four, Kirito breaks up with him, gets with another girl, but Asuna is fine with that and pregnant. IN all endings, Asuna stays with Inoda alone. Please no sharing or whoring out, or, if it must be in the game, let it be avoidable via gameplay.