While I think having a new antagonist for season 5 would be interesting, I feel like the Duffer Brothers should focus on the antagonists they left us with in season 4. I think introducing a new antagonist would be a little risky, given that season 5 will be the last season, and a lot already needs to be resolved without introducing a new antagonist.
I think the Duffers have basically said that there will be no new major characters (antagonist or protagonist) in season 5. They already have enough story to wrap up in 8 episodes, and don't need to be complicating matters further.
PLZ No new antagonists! It's the last season: If they introduce some new antagonist, it just hast to be weak, or die because of a weird reason. They shouldn't play that card to guarantee the season's quality. It don't has to be like: Wow, what an ending... We killed a boring and just lame monster, that the duffers just introduced to introduce some new stuff for the last season. WHY should they "get rid of" Vecna? They built him up!
