If you take out the big four something like this...
Cap "appears" to have been assassinated by Crossbones
(death of Captain America style storyline)
Hulk gets shot into space
(leading into Planet Hulk)
Stark quits
(to become either Director of SHIELD or go into politics or something)
Thor remains in Asgard on the throne
(after deposing Loki in Thor 3)
...and write Black Widow out as being a traitor
(Ultimates storyline)
You've then got the following to choose from already...
Hawkeye
(maybe as Goliath?)
War Machine
Falcon
Captain America (Bucky Barnes)
(...but these may stay more as a SHIELD affiliated team leaving...)
Scarlet Witch
Quicksilver
Ant-Man (Scott Lang)
Doctor Strange
...after which the next lot of recruits would be...
Vision? (a possibility after Ultron has appeared)
Swordsman or Black Knight? ... I'd go for the Swordsman
Hercules? ... doubt it after two recent films featuring the mythological Hercules
Black Panther? ... I expect he'll have had at least a mention by the end of Phase 3.
Mantis? ... not when there's other higher profile characters that could be used.
Beast? ... not happening
Moondragon? ... could be brought over from the GOTG films
Hellcat? ...could work as love interest for Barton, especially in the absence of Black Widow
Two-Gun Kid? ... are you serious?
Captain Marvel ?(Carol Danvers)? ... for me this would have to have an all new origin story featuring the Kree, Monica Rambeau and others.
Wonderman? ... could be introduced when Black Panther brings in his brother The Grim Reaper, and Zemo is part of his backstory so would work nicely
Tigra? ... rather have Black Panther as the feline-themed hero and for some female muscle...
She-Hulk? ... Now this is one that could really work and I'd love to see her in the movies soon
Starfox? ... Thanos connection makes him part of the bigger picture but I can't see him appearing really.
Namor? ... never really liked the guy but I could see the Atlanteans appearing
after the Inhumans have mentioned their existence.
Doctor Druid? ... Doctor Strange performs the same function so i doubt it.
...take your pick
