Well, the big cameo that Paul Bettany teased a few weeks back that’ll appear in WandaVision, was himself! Yes, the big cameo was White Vision from episode eight.
Here’s the confirmation from Bettany:
I got to say, this was the best troll moment I’ve seen in a long time. What sold it was when Bettany said that it was an actor he always wanted to work with, but no one knew he meant himself. I’ll be honest, I’m even laughing while I’m typing this out. So yes, it’s no one from the Fox universe or any other characters that we’ve seen before that he was mentioning in a previous interview.
Who knows? Maybe there is another cameo in the WandaVision finale. We’ll have to wait and see.