I've stated before
1. Unearthed Arcana 4e which includes the following:
a. removing the +1/2 level bonus to skills
b. reintroduces skill points
c. breaks down several of the skills to be less broad
d. a system for handling paragon and epic levels without paragon paths and epic destinies
e. long term injury using the disease track
f. action points that work like true20 conviction/mutants and masterminds hero points
g. the mechanics and math behind building powers (e.g., how much is a push worth)
h. reworking milestones to be more story oriented rather than encounter based for those games that are not based around the dungeon and have infrequent combats. (Rel hit on this early after the release of 4e)
i. something to help differentiate between magical healing from divine power and the warlord's healing (as brought up by Ari on these boards).
j. I wouldn't mind alternative to Paladin's Divine Challenge
k. an option to remove hit points for a True 20/Mutants and Masterminds Toughness save type mechanic
l. Adding a mutants and masterminds type complication system for additional action points
m. non-armored clerics
2. Class supplements formatted like 2e Complete Handbooks and, for 3e, Green Ronin Master Class series. An in-depth focus on an existing class, existing race, new class or new race. For classes, show how to build archetypes from cultures, movies and myths with the inclusion of new builds and powers to support them. For new races, again focus on one race and give variants for different environments and cultures
As a DM the above give tools for campaign building.
As both a DM and player, it would allow me to ignore classes and races that I do not like rather than passing up on a whole book, because only one or two elements that I do want (a major reason I did not buy WOTC 3e supplements and don't want to invest in 4e). Furthermore, having things for a class parcelled out over many supplements is annoying (again, why I stopped buying 3e products and refuse to invest in 4e). A single in depth book means less jumping between books during character creation (and as a DM makes it easier to list which options are and are not available for a given campaign)
And, honestly, I would hire Steve Kenson to write a good Shaman supplement.
3. A PHB/ Heroes of product that has the following
a. races: dwarf, elf, eladrin, gnome, half-elf, half-orc, halfling, human (maybe, Lizardman and/or half-ogre as well)
b. PHB 1 classes, but replaces the Warlock with either the Bard, Druid or Shaman (and, maybe, drop the Paladin for a second from that list)
edit:
c. a new pantheon. in my opinion, recycling deities from other settings from previous existing settings is lame.
4. a single demon book that includes:
Demogorgon, Juiblex, Orcus, Yeenoghu, Lolth, Baphomet, Fraz-Urb'luu, Graz'zt, Kostchtchie, Pazuzu, Zuggtmoy, Dagon
the quasit,
Sub Demon: manes
Demi Demon: alu-demon
Semi Demon: cambion
Minor Demons: bar-lgura, the chasme, dretch, rutterkin
Lesser Demon: succubus
the type I demon (vrock), the type II demon (hezrou), the type III demon (glabrezu), the type IV demon (nalfeshnee, etc.), the type V demon (marilith, etc.), the type VI demon (balor)
Major Demon: gorristro,
5. a single devil book that includes the following:
Bel, Dispater, Mammon, Belial, Geryon, Moloch, Beelzebub, Mephistopheles, Asmodeus, Glasya, Lady Fierna, Levistus, the Hag Countess, Amon, Bael, Bitru, Hutijin, and Titivilus,
the imp, the lemure,
Least Devils: nupperibo, the spined devil,
Lesser Devils: barbed devil, the bone devil, the eryines, black abishai, blue abishai, green abishai, red abishai, and white abishai, the bearded devil
Greater Devils: the horned devil (malebranche), the ice devil, the pit fiend, Styx devil
6 Greyhawk based on
a. The original folio and the original boxed set
b. Pantheon from Gary Gygax's dragon articles
c. the little cultural bits from the 1e Unearthed Arcana Barbarian
7. Forgotten Realms based upon
1. 1e Greybox set
2. Original FR series supplements
(and Jeff Grubb at the helm).
8. Darksun based upon pre 1e Revised boxed set
9. Ravenloft based upon Realms of Terror boxed set and supplements w/ Steve Miller at the helm.
10. Savage World editions of 4-10 above