Not too much detail, just things like general idea and characters.
I might make one where you were part of one of the villainous teams, or at least just had to infiltrate it or something like that. The battles could be something like in Mystery Dungeon. I've always wanted a game like that.
I also might make one with N as the main character because I'm an N fangirl N needs more backstory. So, either where he went when he flew off on his legendary dragon at the end of BW, or, if that gets more about it in later games (and I do think N's going to appear in Gen 6) maybe something about a younger N, kind of like the Ranger games, befriending Pokemon and stuff.
So, what are your ideas for a a new side game?