phase 4 heralding the introduction of the F4 would be glorious. And they need something big too since a lot of contracts are up after phase 3. Dr. Strange and Antman sure as hell can't carry the universe like the Avengers trinity did, so the F4 could be a nice change of pace. 

I'd base it more closely to the source material to the point Human Torch and Spiderman would be in the same high school or college.

~KL~