*legacy spoilers*
So, the Alina being Fitz's mom thing has been a joke circling the fandom and I was thinking and it could actually be good development for Fitz if it was true. He would understand why his brother joined the Neverseen, and would also understand Sophie more and how a parent's identity can change everything.
So then, he would be able to bond more with her since, if it wasn't already known to every elf, he would be having to keep it a secret from people. Also, then with the cognate thing, they might end up being the only ones who know each other's biological mother's identity. This could help repair their cognate relationship as well as their actual one, whether it is aromatic or platonic.
I think we can all agree that it's pretty likely Sophie's mother's identity will be known to all elves at the end of the series. This would help both deal with their moms' identities being known together and to not go through it alone. Also, then it would mean the whole love triangle (even Dex sorta) have a secret about their mother that has been shared and that affected them directly.
That could bring the whole book together as even match making would be messed up for Fitz as well, so then they have new similarities. Also, Fitz, Sophie, and Keefe would all have different DNA than what they supposed in the beginning, Fitz being Alina's son, Sophie being part of Project Moonlark, and Keefe's parents taking that shadowflux whatever mixture thing it was.