In the Art of The Force Awakens book they have some concept art for a force ghost Anakin that doesn’t maintain a static visage. I rather like that idea, like he’s still atoning for the things he did somehow.
Having said that, the only Vader cameo I ever wanted for the ST was a scene where he comes back as a force ghost and tells his grandson, “not in my name you brat.”
I remember that, especially the quote that talked about it where it said that it was inspired by an idea in the Earthsea novel series where the darkness that’s inside you doesn’t just go away when you atone, it’s always gonna be a part of you no matter what. That was a really cool idea that I wish they’d considered for at least the ninth episode, it would’ve worked really nicely to have Anakin sit down with Ben and just state how wrong the crimes he committed were.