I can understand some retcon to allow more space where we can add more PC races and classes.
In Planescape the faction war will continue but not in Sigil, now "neutral zone" and we can't forget the gatetowns.
My bet is the first Dragonlance 5th Ed will be the updated compilation of the modules, and with an optional list of PCs, for example a female kender. I talked several times about an event linked with a multiverse crisis causing, or explaining, the reason of retcons or even total reboot of D&D settings (for example no-humans within the two, or even a third one or more, factions of Jackandor).
* What if I wanted to add new classes into Dark Sun? For example the shugenja, the warden, the seeker, the ardent, the lurker, the warblade, the crusader or the totemist shaman.