Diversification is good. It is easy to move Dash, LTC and BTC on and off BitShares using OpenLedger. That means that you have to keep crypto in those currencies, as you may loose a lot trading to to them in order to get them off.
However, you can also use services like ShapeShift.io to convert BitShares to many other crypto-currencies.
The liquidity and volume problem is one that will hopefully be solved by posts like this (thank you @heiditravels) that promote decentralized exchanges and get more people to use them.