I see what you mean. Yeah, he could probably switch from Asuna getting NTR-ed to Kirito getting NTR-ed once his affection for Suguha is high enough, but what’s the point? NTR is NTR; gender doesn’t matter. Also, as you said, there’s no foreshadowing in that direction anyway, and it wouldn’t make any sense for her to willingly fall for another guy. That should be clear by now. The only way it could work is if she was forced, which would be damn cruel given that she didn’t really harm anyone, unlike Liz. But again, that leans more toward sadism than NTR, tbh.
I guess I’ll leave it at that—I get bored repeating myself, tbh (it’s not on you).