If they wanted ATJ, they would've gotten ATJ. It's not like he's A-list. The head writer of the show (Jac Shaeffer) said they basically cast him to be the "recast character" that people just sort of ignore was recast in sitcoms from the 90's or so (Aunt Viv from Fresh Prince is a prime example of what she's talking about).
I'm not 100% convinced the door is fully closed on Evan Peters. Remember, the MCU is notorious for fake deaths and fake outs in general. Sure right now if you're asking, i'm gonna go with Peters is just Ralph, but they didn't 100% close the door, either. If they want to revisit it once the multiverse is open, they could easily just say that sure he was "Ralph", but no one inside of that bubble was actually that person. Ralph was just the role he was there to play, right? Even the photo Monica held up was literally a head shot.
Not saying it's going to happen by any means, they just didn't fully shut the door on it imo so if they want it to happen, it'll happen.