After watching the most recent episode of WandaVision, it struck me that now would be great way to introduce Nightcrawler into the MCU.
SPOILERS:
After the Hex bubble expands and turns a bunch of objects and people into circus tents, clowns and the like, could it be that Kurt Wagner is soon to make an appearance? It's already known that Wanda will feature in the next Dr. Strange film (Multiverse of Madness, I believe it's called), and Kurt has some pretty extensive dealings with Wanda, Mephisto, and Dr. Strange. He's one of the X-Men mainstays that figures prominently in those storylines.
Okay, Kurt is a stretch. But man would it be cool if Disney decided he'd be the first of the A-list X-Men to make an appearance.
If not Nightcrawler, and not in WandaVision, which major X-character will be the first to make an MCU debut? I actually think Professor X, Magneto, or Wolverine is a lot more likely, but Disney has been great at throwing curveballs!