MM 1 and 2 updated (I know a whole bunch of 1 is already in the MM however) would be pretty nice (as all the adventure critters and etc - that would super!)
However, the massively-mamothian task of a "cleaned-up" 4e would send me through the roof - and quite probably through the
next one after that!
Something along the lines of :
feat trim - only those who offer meaningful choices and serve a pertinent role
theme review - rebalance all the themes to each other
power trim - same as "feat trim"
magic item trim/overhaul - presume inherent bonuses, balance items against each other, create more of a "reality" to common vs. uncommon vs. rare (perhaps diablo-style : one major/two minor = common; one major + 1-3 minor = uncommon; 2 major + 2-4 minor = rare; as an of-the-top-of-my-head example)
terrain / traps - just have them in a logical grouping with a little "suggest use" bit of text
monster update - use the good math
but! keep the "old" aspect of having major differences in attack power for artillery caught in melee and such kinds of things that were in the MM 1 and 2, but got lost in MM 3+. I like that foes can be "disabled" by "simple"
player tactics sometimes.
... probably something else - but if "just*" that came out... I would by that so hard, I'd probably order 7 copies from pressing the button so hard.
Thinking about all this keeps bringing up how fast 4e was thrown away... And... now I'm sad.
