As someone who doesn’t think Anakin should have a force ghost, I would not be happy regardless of appearance. That being said, controversial opinion, but if he appears it should be Hayden, but just how he looks now, nothing crazy.
I still think a scene between Luke, Anakin and Kylo Ren in Episode IX could work really well. Granted, that a special appearance by Anakin would be fan service, but this would be fan service used right where it plays a role in the story and character arcs. I personally strongly dislike fan service in movies, but it can be done right. Some good examples include Yoda’s appearance in The Last Jedi and R2-D2 showing Luke Leia’s original message.