Thinking about the team. USAgent, Taskmaster, Yelena Widow, Ghost and Zemo are the ones that have already been introduced. Punisher is a possibility considering Daredevil's inclusion in the MCU (the same could extend to Elektra but her status is more ambiguous).
General Ross is the obvious one in the modern day but his actor died so that's a bit tricky. I suppose they could have him become Red Hulk off-screen, and then they just need a voice actor, like how they brought Red Skull back without Weaving. Or they might sub in Abomination, that seems likely considering his return in She-Hulk.
As for unintroduced characters, Ghost Rider would be a good one. Rumors continue to swirl about that character recently. And it's yet to be seen if Deadpool with have any interaction with the main MCU, that's a peculiar case that I'm not holding my breath for.
Winter Solider and Hawkeye have both been associated with the team but they feel unlikely to me based on their current associations, Bucky maybe in the realm of possibility.
So with all that in mind I'm thinking:
- USAgent
- Yelena
- Zemo
- Ghost
- Abomination
- Punisher?
- Ghost Rider??
- Deadpool???
- maybe Winter Soldier (like someone mentioned, he could be the Rick Flagg of the team)