According to a Business Insider report, Apple executives have been dropping hints to this effect. They do note that this is gossip; however, and not confirmed news.
A service such as this would make Apple a direct competitor with Paypal, Amazon, and the like. Apple's 30% per transaction fee is likely way to high for such a service to be successful.
In our opinion Apple could expand the App Store to include Mac OS X desktop applications with some success but delving into the world of Paypal and dealing with fraudulent buyers and sellers doesn't seem like Apple's style.