alrite so let's assume it was a ghost (Yoda should've sensed him as a real presence but w/e) why didn't he attack Yoda? ep XIII confirmed what OB1 said force ghosts are more powerful than their live versions
now that Disney's in charge I wouldn't put it past them to do a retcon of sorts especially after they brought back Maul from an impossible situation I reckon anything's possible
I actually hope they bring back Snoke
they can also bring back Sidious himself - alive - and make him as powerful as he was in the EU (magnitudes higher than Anakin or Luke could ever be)