I think there is still lots of room for altcoin trading site as well as blockchain based gambling sites so i may start one of this if i can have some funding. However running these platforms with investors funding will be quite riskier as we need to provide greater protection of bankroll while processing all withdraws/payments instantly.
Most gambling sites that I know manage two wallets a hot wallet and cold wallet, about 90% of the bitcoins are stored in a hardware wallet that never goes online, the second wallet the hot wallet holds about 10% of the coins and is used to allow instant withdrawals for the users.
Never knew this but it sounds pretty logical and I think its a good method to hold the bitcoin on a safe way these days.
Back in the days a couple of websites really got hacked for their bitcoins not its more difficult than before so that is good.