I don't know if there would be any interest in an exchange with 100% cold storage and delayed withdraws.
Most bank transfer take ~24h, so I'd say people might tolerate if you manage to execute them daily. Assuming you explain the reason well enough.
EDIT: A very-small hot wallet, which would frequently get depleted, but that could be refunded daily too, might be even better. By very-low I mean with an amount that you could assure you can refund from your own pockets in case of a hack.This is what it pretty much comes down to. No exchange should operate with a hot wallet larger than the exchange operator is willing to reimburse out of their own pocket. Everything else goes into cold storage. If the exchange operator doesn't want to reimburse anything in the event of a hack, then they shouldn't have a hot wallet. Period.
At this point, it's not a question of if an exchange will be hacked, it is a question of when, and what the procedures of the exchange will be afterward.