Don't block your user's accounts without valid reasons and give a notice before blocking.
Don't take millions for dollars for each and every coin to get listed.
Find an alternative to hot wallets because they suck big time homie.
Keep the exchange updated with the latest changes. Eg: segwit.
Give access to private keys for users.
Don't give a fuck about governments. Go to a country which would avoid the exchange and its users from any KYC obligation. If it doesn't exist, buy a private island and do so, for all I care.
Keep the UI neat and simple, but convenient at the same time.
Customer support would always be my concern when we do talk about exchange features where they must really be responsive because having problems towards the site cant really be avoided and everything should have corresponding email or announcement on what are the sudden changes that had been applied and about user account blocking its good to hear out whats the reason.
Buy their new island? Impossible thing. haha If they are located on a place where government do need kyc implementation then they wont really have any choice but to go in the same path. I dont expect too much that anytime they can avoid it.