Everyone should be involved to a degree but with the exception of maybe one or two other characters, the main key players should be the original 6 Avengers plus Star-Lord.
Oddly, I only came to this conclusion very recently, after the A2 trailer and Civil War announcement. One of my biggest beefs with the MCU setup is how disassembled the Avengers seem. It feels like there's no team outside of a marketing standpoint, as if they're just a few people who banded together on a few occasions out of temporary common interests and nothing else. First film they argue till the near end, then go their separate ways. Second film there will be tension within the group and the team will apparently fall apart. Third film (Cap 3) they're at war with each other. Fourth and fifth films, they have to re-learn how to work together.
I'm not asking for the team to be their default home like it's often in the comics. They can still be a response team, but it would be nice to feel like they share a stronger bond. Which A2 may as well have to a degree, but in order to not just reestablish it after Civil War but further emphasize it, things should come full circle and end with those 6 key players.
Plus when you look at the pillar characters the MCU's been built on, most of its foundation can be traced back to those particular characters. Every major event in the universe has involved one or more Avenger, Agents of SHIELD in its concept is entirely reactionary to the activities of one or more Avenger, every corner of the shown world (Earth-terrorism, SHIELD, other realms, space) has had connections to one or more Avenger. Star-Lord is by far the only non-Avenger to still count as a pillar IMO, since his perspective is our eyes through the cosmic parts of the world. Hawkeye might be the only exception to the rule due to how underused he's been, but Whedon is clearly working to change that.
Other than that, I can't see anyone else having "primary" status.
War Machine, Falcon, Fury and Mockingbird have been just supporting characters.
The other Guardians, though pivotal in their own way, still don't seem to be as essential as some of the other characters I brought up.
There's no mention of Adam Warlock as of yet, but I doubt he'll be used in Guardians 2 given all the subplots set up in the first film. Even then, I don't see him being such huge player in the game if he's introduced so late. It's more likely they'll tweak the comic story around and give Star-Lord a similar role to Warlock's, which is in line with their adaptation motto as of recently and would relate to the earlier statements I made about Star-Lord.
Some have suggested Drax, but I don't see that either. Aside from him not having the same appeal to the GA as practically every Avenger, he's also one of the less appealing characters in his own team - beaten by Star-Lord, Rocket and Groot. That's not to say he's a poor character, but he doesn't seem to have had the same impact on the GA as the latter 3 who all have numerous memes and quotable lines on the internet.
The Defenders...this one's obvious, given the premises for their shows is to explore the more grounded street-level side.
Strange is arguably as pivotal on paper as the big Avengers, but he still would have only one film appearance by then. Sure, he might be meant to replace Downey, but Downey is sticking around till at least 2019.
Same thing for Ant-Man, Captain Marvel and any Inhuman characters. Too little too late, don't see it happening. Pym may be a major Avenger in the comics, but he's in a completely different place in the MCU.
Black Panther is a tricky one, since he'll have two films by then and seems to be replacing Spidey's Civil War role, plus the recent rumors he'll debut in AoU first.
Quicksilver, Scarlet Witch & Vision are major well-known Avengers in the comics that are still debuting relatively early and can appear in multiple more films, so they also have a higher chance IMO.
So in the end, other than the 7 earlier characters I brought up I only see Black Panther, Vision, or the Twins being important characters.
Oddly, I only came to this conclusion very recently, after the A2 trailer and Civil War announcement. One of my biggest beefs with the MCU setup is how disassembled the Avengers seem. It feels like there's no team outside of a marketing standpoint, as if they're just a few people who banded together on a few occasions out of temporary common interests and nothing else. First film they argue till the near end, then go their separate ways. Second film there will be tension within the group and the team will apparently fall apart. Third film (Cap 3) they're at war with each other. Fourth and fifth films, they have to re-learn how to work together.
I'm not asking for the team to be their default home like it's often in the comics. They can still be a response team, but it would be nice to feel like they share a stronger bond. Which A2 may as well have to a degree, but in order to not just reestablish it after Civil War but further emphasize it, things should come full circle and end with those 6 key players.
Plus when you look at the pillar characters the MCU's been built on, most of its foundation can be traced back to those particular characters. Every major event in the universe has involved one or more Avenger, Agents of SHIELD in its concept is entirely reactionary to the activities of one or more Avenger, every corner of the shown world (Earth-terrorism, SHIELD, other realms, space) has had connections to one or more Avenger. Star-Lord is by far the only non-Avenger to still count as a pillar IMO, since his perspective is our eyes through the cosmic parts of the world. Hawkeye might be the only exception to the rule due to how underused he's been, but Whedon is clearly working to change that.
Other than that, I can't see anyone else having "primary" status.
War Machine, Falcon, Fury and Mockingbird have been just supporting characters.
The other Guardians, though pivotal in their own way, still don't seem to be as essential as some of the other characters I brought up.
There's no mention of Adam Warlock as of yet, but I doubt he'll be used in Guardians 2 given all the subplots set up in the first film. Even then, I don't see him being such huge player in the game if he's introduced so late. It's more likely they'll tweak the comic story around and give Star-Lord a similar role to Warlock's, which is in line with their adaptation motto as of recently and would relate to the earlier statements I made about Star-Lord.
Some have suggested Drax, but I don't see that either. Aside from him not having the same appeal to the GA as practically every Avenger, he's also one of the less appealing characters in his own team - beaten by Star-Lord, Rocket and Groot. That's not to say he's a poor character, but he doesn't seem to have had the same impact on the GA as the latter 3 who all have numerous memes and quotable lines on the internet.
The Defenders...this one's obvious, given the premises for their shows is to explore the more grounded street-level side.
Strange is arguably as pivotal on paper as the big Avengers, but he still would have only one film appearance by then. Sure, he might be meant to replace Downey, but Downey is sticking around till at least 2019.
Same thing for Ant-Man, Captain Marvel and any Inhuman characters. Too little too late, don't see it happening. Pym may be a major Avenger in the comics, but he's in a completely different place in the MCU.
Black Panther is a tricky one, since he'll have two films by then and seems to be replacing Spidey's Civil War role, plus the recent rumors he'll debut in AoU first.
Quicksilver, Scarlet Witch & Vision are major well-known Avengers in the comics that are still debuting relatively early and can appear in multiple more films, so they also have a higher chance IMO.
So in the end, other than the 7 earlier characters I brought up I only see Black Panther, Vision, or the Twins being important characters.