The “Many Worlds of DnD” article by Mike Mearls came out today and unlike many responses I’ve seen I’m not particularly happy with the article.
Mearls opens the meat of the article with the sentance “To begin with, we’re making some tweaks to the cosmology to reconcile the differences between various editions and worlds.” He then goes on to explain how what that means is they are returning to the Great Wheel and making some tweaks to the Inner Planes to keep the Shadowfell, Feywild and Elemental Chaos from 4E. The article then wraps up by saying “Ideally, our approach allows Eberron, Forgotten Realms, the world of the Nentir Vale, Greyhawk, Mystara, and your own campaign setting to work with the basic assumptions we make about the planes.”
There are several issues with this, the most important of which is that “one size fits all” has always been a bad design approach and one that TSR and later WotC has been poor at using. Krynn and Athas are two classic settings that had their own cosmology that was wedged poorly into the Great Wheel. During 3E Eberron’s cosmology was wedged into the Great Wheel and of course in 4E the default setting was married strongly to the 4E cosmology with no allowance for the Great Wheel. Then there are Mystara, Spelljammer, and others that have limited, poor or no connection to the Great Wheel.
I would suggest that the best solution for WotC would be for each setting to have its own cosmology and to abandon the “one size fits all” approach. The important thing about having unique cosmology for each setting is that creates greater design freedom for each setting and through that allows greater setting consistency. Then in material intended to connect settings, such as Planescape and Spelljammer include advice for DMs on how to incorporate the individual settings into those larger settings. This could be done through Dragon articles or other downloadable content as well.