Seems like an interesting idea. You would basically become a broker, lending your own funds to allow customers to use leverage, charging them interest to do so. Along the same lines you could also allow customers to short sell by lending them shares from your own inventory.
I was thinking at first of being more of an facilitator between lenders and traders, and letting them work out their own interest rates and margin requirements. But until there's more interest, I suppose I could start by lending my own coins (although I don't have much to lend at the moment).