I know Harry Potter (who doesn't?) but I'm not so familiar with Sherlock... I've heard of it, but haven't watched more than an episode that my friend showed me.
Have you read A Court Of Thorns and Roses? I'd be more open to trying something in the world it's based in than a Harry Potter thing.
I think it could be fun... Like a world where the Fae hide from humans or something, but then a human finds out and gets dragged into the mystical magical world