Though I'm not a fan of Sophie Turner's acting, I'm still excited for this movie because the Phoenix Force is arguably the most powerful being in the Marvel Multiverse that we will ever likely see on the big screen. Maybe Galactus, but it's debatable which of them is more powerful. And I'd give it a snowball's chance in hell they ever introduce Eternity, Infinity, Death, the Beyonders, the Living Tribunal, or the One-Above-All directly in a Disney movie, largely because those are story-lines too complex to fit into Marvel Studios formula, but also because the budgets for such a film would make Avengers: Infinity War look like pocket change. Plus, they've already deviated too much from the comics - such as Drax in the comics would stomp a mudhole in Thanos, who without the Infinity Gauntlet is a badass mortal, but is definitely mortal.

So the current film is pretty much the Infinity Gauntlet story arc from the comics, which leads to the Infinity War later, but I can't see them introducing characters as powerful as Adam Warlock, let alone any of the cosmic entities I noted above, if they're painting Thanos as such a big bad.