I don't think the game needs a reboot, the story of ARR is fine, but I would streamline the patch series between ARR and HW, I can imagine most people quitting then.

I would also adjust what abilities you get when, but I think that's already happening.

A lot of people have left wow to play/try FFXIV. Getting rid of that patch series slog will be the best way to retain them.

I'm fine with only two classes, I would rather they have 2 good classes that are fun, than 5 poorly thought out classes.

Maybe they will release a third mid expansion, we'll see.