One of those "profession" AUs: Sherlock is a chemist who develops custom perfumes. He uses his genius to deduce what exact blend of scents each customer needs for their own body chemistry, and he's world-famous. He and Mycroft own a fancy perfumery together - maybe Mycroft runs the business side of things, or handles all the mass-produced perfume lines?

Either way, I'd love to just see Sherlock lording it up in his expensive perfume shop, deducing people and pulling the whole "you don't have any choices here; I will give you what I think you need and you're going to like it" thing.

Totally a fan of pretty much any pairing romance, so feel free to include any canon character as a "customer" who doesn't react to Sherlock's rudeness the way he's used to :-P