It sounds like Bancor is going to be in competition with the Waves Platform. You can create your own tokens on each network and they can be exchanged within the system. Why use Bancor and not Waves?
I would say that Waves is somewhere between an Ethereum and a Bancor. It provides the infrastructure to create tokens and eventually smart contracting capabilities. Bancor's focus is on providing liquidity through their algorithmic pricing and removing the need for exchanges. Waves doesn't offer this functionality, but rather uses the DEX to match a buyer and a seller.