What I would love to see in the next version of D&D 6 is a much lower frequency of:
1) dark vision. The poor races that do not currently have it are at a disadvantage compared to the majority that have it. And in a dungeon, it's common for the party to have to light a torch for the human PC only, while the other 3 would be fine without it.
2) magic in the form of spells. All classes currently have access to magic in the form of spells. I would like the spells to be distinctive of rare classes that might use it. I imagine for example the classes of ranger, fighter, rogue and barbarians without magic; and even the paladin could easily be differently designed. Then monsters too could have some powers, but fewer spells.
Regarding this last point, from the 4th edition, I would like them to bring back interesting powers for monsters, which are not necessarily spells. That was cool.