I guess I disagree that they “should have” made an appearance at all. That would have been pure fan service. If there was a place in the story for either of them, then sure. But there wasn’t, so trying to force an appearance where it isn’t organic is just going to be…well, forced, and unnecessary. That would have been true if Johnson had decided to toss Obi-Wan in there just because he felt obligated (see: Leonard Nimoy in Star Trek: Into Darkness) and it will be doubly true for any fan edit trying to jam him in there just because the editor thinks he needs to go somewhere.