All it takes is one phone call from Ebay to Bitbay and there is no stopping after that. Obviously, Bitbay is trying to set up their own platform as a competitor to Ebay and Openbazaar (which is still beta) but there is possibility that Ebay might approach Bitbay to join hands in near future.
If eBay really implements BitBay, than this coin will have the highest userbase of all coins i think.
Edit: Let's better say it will have a good operational area.
Having existing exchanges offering the 'Bitbay Contract' as an optional security layer for trading is going to be great. You negotiate the trades on Ebay, Craigslist and whatnot and you secure it through Bitbay. Beautiful.