also, what if, when Sherlock and John first meet, it's blatantly obvious to John that Sherlock is a gem, (cause his is on his forehead) but John doesn't let on that he's also a gem, and it's the one thing Sherlock can't deduce about John (partly cause of all those darn jumpers) and one night John invites Sherlock to dance and Sherlock gets all confused because "dancing is for fusion John, you're not a gem" but they dance anyway and end up fusing and Sherlock is just like "um, what the hell?"
Dude, you have great ideas, too, write a fic!!