She also uses Ami's lust name. I assume it's just because those are the game's first two lust names (the only ones at that point?) and Sensei's brain is free associating.
I'm not sure what you're asking here, or if you just wanted me to comment on the Sekai/letter T thing. I personally think that both Maya and Ami are dream babies for reasons independent of this passage, and it could be interpreted to support that, but as you point out neither AmIOkay nor Sensei outright states that anyone is a dream baby.
AmIOkay doesn't just represent Sekai in this event, since Sekai is a big incest fan whereas AmIOkay disapproves.
This is even more confused though, since refusing to have sex on her best friend's bed points to Maya, but if she was just the Maya we know, having sex with Akira wouldn't be incest no matter what bed it's on. I think Akira's mind is just jumbling a lot of things together, and AmIOkay is some combination of his thoughts regarding Maya, Sekai, and Ami here.
In regards to the girl whose name begins with the letter T, I do think that refers to Sekai, though maybe not directly and maybe not exclusively; it could be someone outside the simulation that Sekai is a reflection of or something like that. The part I've always been opposed to is the idea that the T stands for teacher - I still think it stands for something that we don't know.
Actually, there was something in the last update relevant to this. Previously, some people argued with me that Akira knew her as "Teacher" because she was an English teacher and thus used an English title, but in the alternate timeline she revealed that Akira called her Sensei, so that theory is out.