The past has shown that everyone, even persons who run e-wallets and currency exchanges, severely underestimates the amount of security such an endeavour requires.
There's a hundred questions you should ask anyone who asks you to keep care of bitcoin. How large is the hot wallet? How is the offline wallet stored? Where's the source code? What hardware does the service run on? Who are you? What will you do when someone steals your hot wallet? What monitors do you run to make sure the books add up?
So, nice idea, but please make sure this is actually going to be safe.
(BTW there seems to be a way to escrow bitcoin where a third party decides if the transaction should pass, but that third party never gains access to the bitcoin themselves, I haven't read the details of it, but that would seem perfect for this sort of thing)