I don't think they can unify the fans. It's not like 2000 when most D&D players had drifted off to other systems or stopped playing altogether. Both 3e/PF and 4e seem to have very active fan bases. And at least some portion of the PF fan base thinks WotC is the devil.Without turning this into an edition war, what are the fault lines in the fan base that wizards will need to bridge in order to unite everyone under a new edition? Let's say you have a group of players who each hail from a different edition and are representative of that edition's fans. What problems will you run into trying to customize a game they can all enjoy.
That said, when I think of fault lines, the following occur to me:
* "New"/"weird" fantasy vs Tolkien-esque "traditional" fantasy.
Once upon a time, 3e came out and was charged with being too "anime" or "dungeonpunk" or "videogamey." Years later, 4e put dragon-men and devil-people in its PHB1, and things only got worse.
* Quirky, individualized subsystems vs unifying mechanics.
* Balancing Flavor vs Crunch.
* Rules-lite systems vs systems that allow for heavy customization (and customization's overbearing cousin, optimization).
* Everyday magic vs "magic is rare and mysterious."
* Interesting combat options vs "I swing my sword, again."
* Heroic PCs vs PCs that run from a house cat.