If they do create their own, it'll be a marketing stunt. They don't need a coin! They already successfully accept payments all around the world with the Starbucks app / giftcard system which integrates well with their contests, rewards and "star challenges". The ironic thing is that many people I know have been purchasing Starbucks with Bitcoin for over a year (through crypto-debit cards like TenX or buying Starbucks giftcards with Bitcoin on sites like coincards.ca).