I know ROTJ:R is still a long way off, but I had a dream last night that inspired an interesting idea for the end with Anakin's Jedi Spirit appears next to Obi-wan and Yoda. The idea is to keep Sebastian Shaw, but somehow make his hair seem less grey with a bit of coloring that almost matches Hayden's.
ROTJ:R concept of Sebastian Shaw with younger Anakin hair coloring
image from GOUT ROTJ
The logic of this is that Obi-Wan and Anakin are supposed to be about 15 years apart in age.