I'm really not seeing how people think Nanjou will reciprocate in any way to Riri. To me she is 100% fully devoted to the Nurse (forgot her name) and has shown zero interest in Riri romantically. Not only that, the nurse is 100% into Nanjou. I mean did anyone questioning the ship(s) actually read the last chapter before this? They both are totally smitten (Nurse+Nanjou that is) and Nanjou CLEARLY isn't into sharing her love.
Uda has no feelings (romantically) towards Nanjou, not even a hint and has proven to be very jealous over others getting close (ribbon arc). Rriri has been pretty adamant about Nanjou loving only her, even going so far as badmouthing the nurse.
To me the most logical thing will be a massive confrontation between the three (Nanjou, Riri, Nurse), or something that launches Riri into a wave of depression. Or maybe even a final heart-to-heart talk between Riri and Nanjou that will give Riri closure (this is probably most likely as it fits the theme of the manga). I see absolutely zero chance of "poly". Honestly thank goodness. It would just not make any sense, also tbh I dislike it.
I would also like to point out Riri's wish for Nanjou to notice her just once. Just as Uda used her "once in a lifetime" wish, Riri used hers. This further supports my hunch that they will have a heartfelt talk and resolve things. In any case the wait resumes.