Back before WWDC 2013 rumors started to spread about iOS 7
providing access to third-party keyboard makers. This rumor might
originate, in part, from a question Tim Cook answered at the D11
Conference about third-party APIs (application programming
interfaces). It might also have to do with “leaks” that came out
just prior to WWDC claiming at least a couple Android keyboard
makers were getting ready to port to iOS.
WWDC, however, passed without mention of third-party keyboards for
iOS (but with an awkward car demo!). Whether third party keyboards
were never on the agenda, or the “leaks” got them kicked off the
agenda, or they may indeed be on the agenda for a future event is
tough to say. All we can say is that Apple hasn’t announced any
third-party keyboard support for iOS, not open to every developer,
not tied to limited partners, nothing.
My understanding is that third-party keyboards were never on the agenda for iOS 7, or at least they were never planned for what was announced at WWDC. Nothing along these lines got yanked. The main issue Apple faces is security: a third-party keyboard would “see” everything you type, in every app you use. Regular apps you download from the App Store are sandboxed; third-party keyboards couldn’t be sandboxed in the same way apps are.
Plus there’s the user interface question of how you’d install them. Right now, everything you download from the App Store is an app that shows up as an object on your homescreen. Where would a keyboard go? I’m not saying these are particularly hard problems to solve, but just that Apple hasn’t solved them, and so thus there are no third-party iOS keyboards.