Too many people would be pissed if it was Hayden (canonizing the 2004/2011 SE), and too many people would be pissed if it was an actor who looked like Sebastian Shaw (canonizing the 1983 TC/1997 SE/giving a middle finger to the PT).
It’s a no-win situation to use Anakin’s ghost.
How would you feel if they had Ewan McGregor in old makeup (to look like Alec Guinness) make a brief appearance as Obi-Wan’s Force spirit?