I would prefer F4 - this would include Doom, Surfer, Galactus, Thing vs Hulk etc
Or the X-Men - Wolverine vs Cap, Storm and Thor, Professor X vs Dr Strange.
I'm thinking that they could have been active around the same time as Pym. Perhaps early experiments with the Tessaract. Perhaps play up the 50's or 60's sci-fi elements. Perhaps an Invasion of the Body Snatcher's feel. Have the movie villain be Annihilus instead of Doom. Have the team disappear into the negative zone for the end of the movie, needing to close the door from the other side. For the after credits scene have some fall out from the Infinity Gauntlet, re-opening that portal.
In short, I need an excuse to have Annihilus for an Annihilation Movie. I want the Fantastic Four chunk of the space opera, sure they could make a deal like they did for Ego. However I like the idea of the next saga being a build up to the Annihilation wave, between Captain Marvel, Guardian's of the Galaxy, a Nova movie, and with the FF, A solo Surfer/Heralds of Galactus Movie.