There's always scope for a incremental K-3 update like a K-3 II, or K-3s, I guess, with minor engineering changes, maybe some new controls or design elements, plus one or two cool new features (eg hybrid EVF/OVF viewfinder) and some bug fixes. There is plenty of precedent for it. Makes marketing sense sometimes.
But IMHO, at the moment Pentax has nothing in hand that's big enough to warrant a completely new APS-C model. No one else seems to be rolling out any significantly upgraded 24MP APS-C sensors, for example, or making available other dramatic new technologies that Pentax would be likely to use.
I think that APS-C development has hit a kind of limit now, particularly with sensors (no one seems to want to push APS-C past 24 MP, for example, and all the current 24MP models from Sony/Nikon/Pentax perform pretty much the same in terms of IQ). So the only significant way forward for Pentax from the K-3 onwards would be to go full-frame.