mystery box.
the more i think, the more genius it kind of is. JJ was written into a corner, RJ had left him with nothing, but they always had Palpatine who had gone unused at that point. they couldn't bring back Vader cos Kylo is the Vader, but they could do this. but fans would get upset?
that's the point!
IMO one of the things they took away from TLJ was that trolling fans and sometimes just straight up ignoring canon results in more fans talking about your product. whether they are arguing or not doesn't matter, they are keeping your product relevant, making marketing people fall in love with you, "the metrics are so good, baby." this is why Rian was liked by them, and the last film bought them a whole ton of social & access media cred. trolling fans is a way to "keep it relevant", one of goals touted as a success by KK. they are not dumb, they have seen how fans trolled George during the PT, it is all part of the game. why not leverage that? have fans do the marketing for you, basically. have them sometimes write the films too.
so JJ is doing this movie, and it is guaranteed to have tons of fan service. he has to be allowed to do a few things that just fly in the face of canon & get fans talking & keeping it relevant. why not use that on the Emperor?
gotta admit, it's kind of a smart gamble, in a cynical capitalist way.