I think if we get one villain for each original Avengers, that might be OK, but it would be a bit hokey. I'd be fine with USAgent, Yelena Belova, and Abomination at least, but let's see other villains come back that didn't die....like, uhm... Hmmm. Zemo? And Mordo! How about Ghost, she's still gotta be alive even after the Blip.
I do wonder, if Valentina is working for Ross and we get a team of anti-heroes as the Thunderbolts, named after General "Thunderbolt" Ross. It didn't happen like that in the comics but it would be a neat way to work that out in context of the MCU, and it gives us a reason to see Ross eventually become Red Hulk, if William Hurt is up for it, though I understand he's not as spry and young as he used to be, though someone younger could do the on-set mocap and he could just be the face/voice for Red Hulk.
It seems like the MCU is gearing up towards both a new Avengers team and/or the Young Avengers, and some sort of anti-Avengers team (Dark Avengers or Thunderbolts). I think if we get both or all of these teams, it would be neat to see them all have to team-up in a sort of Secret War(s) battle against a villain like Doom or Kang. Seems like the best way to one-up a climax like Endgame, especially if the X-Men and Fantastic Four are also involved. Then again, they could do the Onslaught storyline and I would die happy, and that would give them a good reason to reboot Avengers characters with new actors if they so choose.
Also, I'm still wondering if they're going to do an A-Force film once She-Hulk gets off the ground? Would love to see her, Captain Marvel, Rescue, Wasp, Sif, and maybe a couple more in a film together!
-Marc.