So there's rumors now that not only Luke will show up but the Disney+ show might have some flashbacks/visions? with Hayden Christensen as Anakin.
Bringing Hayden in to a Disney project has been of course floated for a while-there's concept art of him as a sort of mixed Anakin/Vader force ghost and of course he did do the vocal cameo for "Rise". Hayden Christensen seems to mainly be semi-retired from acting (although he does an occasional small-scale action movie or romantic comedy) but maybe he'll show up to film a few scenes. He also doesn't seem to have aged that much-he maybe looks a bit thinner now (He kind of bulked up a lot for ROTS) but apart from that he more or less looks the same IMO.
Of course a young Luke (not played by Hammil) does makes sense as well as he was pretty much Obi-Wan's primary purpose for being on Tatooine in the first place.. Plus the original film pretty much did infer that they knew each other at least casually, although of course Ben doesn't tell him about who he really is until it becomes relevant (and even then of course he doesn't tell the whole truth).