I think Marvel Studios want to keep the 'wow' factor whenever they make an Avengers film. And most of that 'wow' comes from the fact of seeing various characters appearing on the screen at the same time.
If you start to put more than one Avenger into individual franchises you lose a bit of that mystique. You dilute the 'wow'.
There may be mentions and nods and winks but apart from (maybe) a post credit sequence I don't see any major appearances.
I feel that the more seperate you keep each individual franchise the more special it is when they do eventually 'assemble'. I would also like to see (although it would be almost impossible to do successfully) each franchise have much more of its own individual character - perhaps seperate genres. (Thor with a fantasy epic feel, Cap as a war film, Ironman as a near future, corporate espionage film, Hulk as a horror film - you could do Dr Strange as a horror flick, Powerman and Ironfist as a exploitation flick, etc, etc).
The idea of trying to mix that all together seems very exicting to me. Mind you, Fiege has said and made the conscious decision to tie the films together in terms of look and tone which is probably the much more sensible approach.