I guess cougar towns already kind of happened... sort of (?). But anyways if you could choose what would you want the other show to be.
I've read a lot of people say that a cross over with P&R would be good. I remember an interview with some of the actors where they said that they wanted Abed and Tom to be cousins and that's how the two shows could be connected.
I've also read some comments that people have made where they want Pete and Trudy, from Mad Men, to be Annie's grandparents (So I guess Tammy would be her mother? hey it works) (also part of me would also like to see this happen).
I realize that there has been a ton of TV references made on this show but those are just small technicalities