I think we are about to see a new market split. If the changes aren't enough to justify the new purchase, people won't buy in immediately. It will be a slow purchase because of compatibility. IF there are too many changes it will split because if the changes don't benefit the game or harm the backwards compatibility element, if they really try to advertise that, people won't buy in. They brilliantly marketed 3.5 enough to make it seem like it was really an upgrade to 3e, they were able to talk about the gaps in 3e and what they were doing to "patch" them while giving lip service to compatibility that really wasn't there. They are kind of in a weird space with this because its a different market and D&D is no longer really a part of the RPG market, being it's own thing with how it outclasses every other game. New fans might just gobble it up but they might also be very slow to pick it up. I don't really intend to as I am fine with 5e as is and if the changes are as small as they say, ehhh, maybe one day if my group insists.