I'd like to see a lot of what's been mentioned: Chase rules. Mass combat (ideally on multiple levels: from skirmishes between a few dozen all the way up to battles between Alexandrian armies). Naval combat rules. Fun & playable domain (running a territory) rules (which could maybe be generalized to "running an organization", so you can cover guilds, temples, etc.).
Of course, there's no way they can fit all that stuff in the core rules, and if they haven't already started some of it (or at least have some Really Good Ideas), it would be hard to do well in the few months they have left. So, really, I'd be happy if they put a bunch of that stuff out after the core rules (I want it sooner rather than later, of course, but I want it
good most of all). So, WotC dudes, consider this brainstorming for what to do between Monster Manuals and campaign setting revisions.
One thing that I do want fixed in the core rules: the lighting rules. They're kind of silly right now.
"Shadowy illumination" is very obviously another way of saying "low light" -- yet low light vision
doesn't help you see any better in it. If you're in a room lit by scattered candles, the whole room could be at "shadowy illumination"; yet the elves will have the same 20% miss chance the humans do, because all low-light vision does is let you see twice as far (and if you can already see the far wall...). Gah! Just say low light vision lets you treat areas of "shadowy illumination" as regular lighting, and adds an extra increment (equal to the base radius) where low-light vision lets you see as if it were "shadowy illumination".
(I'm not sure the "light source gives x feet of regular light and then x more feet of shadowy illumination" makes much sense, either, but I can live with it a bit as a simplification. Maybe just lower the fairly generous radiuses a bit? 20 ft. to 15 ft? <shrug>)
Oh, and it would be nice if rogues and assassins (without darkvision) lurking in dark alleys could actually use their abilities (i.e., sneak attack) to mug people effectively, too. Which isn't necessarily related to the lighting rules, but still. (Maybe the miss chance -- if that still exists -- is also a chance that the sneak attack just won't work?)
And finally, come up with a better name than "shadowy illumination". "Low light", maybe.
(And
then they can fix the
darkness spells, as KarinsDad suggested.)