You might be right that they will come up with some contrived background story for Blaine from his mum. Her working at Mary Kat (Kay?) cosmetics kinda already hints at this (like his clothing and gelled hair).
But what will be more interesting is if they’ll also cast Blaine’s dad. And if so if he will be the loving, though maybe a bit distant, father that canon tells us he is (who wanted to build a car to bond with his son, allowed him to transfer schools to be with his boy(!)friend, who stayed up to hug Blaine all night after the school shooting, and who apparently never stopped supporting Blaine financially when he bought an engagement ring and went to live with his fiancé in New York), or if RIB will retcon Blaine’s dad and make him the coldhearted, homophobic and maybe even abusive asshole that Klainers love to portray him as, so they can feel sorry for their precious Blaineydays and conveniently excuse all his actions because of his horrible youth and home situation.
I’m also curious, if they show both Blaine’s parents, if they both will be white, or if they’ll have one of them be Eurasian. We know Blaine’s brother is 100% white, so unless Cooper is Blaine’s half-brother (which they never alluded to, while they made sure to mention several times with Puck and Jake, and also Kurt and Finn, that they were not real brothers) Blaine should be white as well. We’ve got nothing but a few vague hints but it was never established if Blaine was a POC.
Whatever, I’m not interested in Blaine, never want to see his face on my screen again tbh, and I’ll probably won’t even watch any scenes he’s in (not even if he shares them with Kurt), so I also give a rat’s ass about his family. Although I also freely admit that if anything happens with Blaine’s parents that involves Kurt and purposely tries to retcon or excuse Blaine’s horrible behaviour I’ll probably hear and rant about it, lol.