Low trading fee and high volume. TRON is good to trade but I wish to see the trading fees reduced. With the amount of volume of TRON, the exchange should be able to gain still even with low withdrawal fees.
Pay out a percentage of staking rewards to depositors of POS coins. This would allow customers to "hold" the coins and reap staking rewards while simultaneously setting limit orders in case of a price increase.
I'm not aware of any exchange that does this -- and maybe there's good reason for that. I haven't thought through all the logistics.
Binance does that for few coins/tokens, It would be nice if they did it for all the POS coins. Coinbase has started staking service for Tezos and they might add more like it. I personally like staking by myself for the obvious reasons.
And they give the GAS for NEO as well. Most of the exchange does an airdrop of some tokens I never knew. I like that but should just pick the ones with good value.