my money is on trying to do both and alienating both..
as I gaze into my crystal ball (the one that hasn't hit lotto yet) I divine they will try to change enough to 'fix' the game for modern sensibilities and enough that buying the new book is needed enough so they will sell them. However I bet they will try to keep so much the same to pay lip service to "it's all the same system" that people who WANT systematic improvements and changes will find the changes half measures at best.
Ex: I bet they rewrite every race to be the new way but at least 2-3 of them will end up different enough that you can't just say "oh this is just tasha updates" and the same with classes.