Very simply I will use whatever system, be that BTS, some ETH solution when that comes along, or some multisignature solution that correctly replicates what I get at poloniex or bitfinex. Where I can store, safely on bloackchain, my crypto assets and earn interest from loans that I make until I have decided to sell them on the exchange or remove them from the exchange.
I can't see getting anyone to use Bitshares over exchanges without the incentive of interest. Nor can I see a use case where I could convince a merchant to store dollars in Bitshares over Paypal without interest on those dollars.