The black market is already well established on Tor, so I'm not sure if OpenBazaar will result in growth in such markets, or just a shifting of some existing business from Tor to OpenBazaar.
It is well established, but plagued by issues relating to centralisation - exit scammers, law enforcement infiltrating markets, people stealing bitcoins. Each time this happens, growth is damped as buyers and sellers shuffle over to new operators. OpenBazaar would revolutionize this.
