I think I would prefer things to help DM's cut down on preparation time rather than new rules/options/settings etc...
For example... it may already have been done (possibly in earlier editions)... but I would like to see nice glossy NPC cards.
Kinda like the ones you get with the D&D minis - but with more of a MtG type look. They could have a nice colour pic on the front... with a few mannerisms/traits etc. beneath it, and a statblock on the back. Each of the things listed need be no more than a few words or sentences (Eg. Traits: Sincere, Kind hearted, Perfectionist; Mannerisms: Often strokes his beard whilst talking; Secret: Collects forbidden tomes...... etc.....)... just a few ideas to get you started... and they would be great for various town guards, inkeepers, merchants, beggars, shopkeepers, scholars, millers, farmers, etc.
Hell... they could even make them 'collectible' and I'd still give them a shot
Then if I needed to populate a small settlement quickly (or on the fly)... I could just pull out a few relevant cards, and put them all in a few of those clear folder things (that contain 9 pockets to put collectible cards in) - and I'd have a reasonable starting point... all ready to go in a matter of minutes.
Potential for 'expansion sets' could include similar cards for various settlements... just a picture and a brief 'boxed text' kind of description on the front, and the stat's on the reverse. A similar thing might be feasible for individual buildings too (but listing things like an inn's goods & prices, on the rear).
(note that this NPC card thing is something I do for my own games... but it obviously takes up time creating them in the first place... time that could be better spent on adventure plots etc...)