A D&D cartoon, if done RIGHTGDIT, could be very amazing. To my way of thinking the unquestionable ideal venue would be Planechase with frequent visits to other camp settings, heavy on Eberron and Greyhawk with fewer visits to settings like FR and DL (the former because it's too expansive and the latter not enough so). Spelljammer is a bit too corny for audiences to accept, I think (but then I was certain they'd never pull off a Thor movie so who knows), but picking only one setting would be a tragic waste of the immensity of the canon.

Mind flayers. I want GD mind flayers for the main villains. Pretty much impossible to improve on, though ideally others would be used as well. Some of the best storylines like Temple of Elemental Evil could use a nod as well, but it'd be neat if the story didn't follow these well-known plots so much as cross paths with them, giving the impression of huge machinations going on which the players only touch upon.