I think the idea of a decentral marketplace is very good. But the problem i see is, that u dont need a special altcoin for that. Like ebay, where u dont need only dollar to sell and buy things. So ... what could be the future of bitbay's? U can make a marketplace trading fee. And all bitbays holder get some of this fee. So would be a reason to buy bitbays to get some interest.
It's going to be similar to openbazaar as far as my understanding. It's going to be more secure plus faster because of smart contract. No fee would attract more sellers. Price will have no choice and it'll have to go up when everyone is buying bitbay so they can purchase things on marketplace.
Next question could be seller would sell as soon as they get bitbay. Solution to that is hedging just like money marketing and btc has it. Pretty simple and smartest way to do it.
No paypal
No fees
Fast transaction
That's the dream website of sellers. Openbazaar is still in beta and my guess is (I could be wrong) that bitbay is trying to set up marketplace before openbazaar goes online (begining of next year or end of this year)