Isn't it the case that as long as these exchanges keep acting so bank-like (holding on to people's keys, possibly using them for trading or fractional trading or what you would call it) they will keep having these problems since crypto is so prone to "bank"-runs. There are no real reason for any of their customers to keep their money with them as soon as there is even a hint of suspicion of illiquidity or insolvency. In real banking you a lot of the time atleast need to go and take your money out but in the crypto currency world that can be automated.

I feel like the only real way they could be run while avoiding this to only work as a broker to make dealto purchase coins available to users and possibly also sell a wallet software or something that is mostly a frontend and no keys/money is kept with them. Then they are only ever able to trade on the exchange fees and purchase money for the wallets they get. But I guess such a reasonable way to run a buisness is no way to get filthy rich...