That's a great idea!
I intend to get foam boards at some point, right now my design wall is just flannel tacked to the wall. It works, but it could be better. I know the local Joann's carries this headliner fabric. I just might have to give this a try!
I have a curtain wire I'm going to put up over my design wall, with a curtain I can pull if people are coming over and I want to hide whatever is in progress. (Either because it's not working out, or because it's a gift for someone that's coming over!) But I like your quilt idea too.
And, I'm sure this was just a typo, but I cracked up at "room decider" - it's pretty appropriate actually; it "decides" where the room boundary is! I might just start calling them that from now on. LOL