While not as quite "anyone can do it" as pg. 42 we do have a stunt system in the PHB:
True, but that system is limited in scope and easy to forget, not to mention being only really useful to people with Acrobatics training. I want a stunt system that jumps up and down and yells "Hey, use me!" every time a player looks down at his/her character sheet. Hence the stunt points. (To further encourage free-form stunts, stunt powers should have moderately specialized utility; e.g., Turn Undead.)
Further thoughts:
With regard to skill challenges, redesign the skill system with them in mind. Take the example skill challenges in the DMG and build on them to create a set of challenging, mechanically interesting "encounters," while at the same time making them more generic and applicable to different situations. Design them around being referenced at the game table. Ideally, any time a noncombat situation comes up, the DM should be able to crack the DMG to the appropriate skill challenge, "fill in the blanks," and go.
Some examples:
- The Plea for Aid: Talk an NPC into helping you.
- The Infiltration: Sneak the party past guards or sentinels.
- The Interrogation: Get a prisoner to talk.
- The Journey: Travel across a stretch of wilderness.
- The Bargain: Negotiate an exchange of goods and/or services.
- The Search: Locate a hidden place or object.
- The Escape: Get away from pursuing forces.
(Many of these already exist in the 4E DMG; I want to make them bigger, better, more interesting, and easier to adapt.)
Add a Backgrounds chapter to the PHB, in which you choose your character's background in broad strokes. This includes things like non-adventuring skills, profession, and so forth. Start with the background system in Scales of War and develop it - while at the same time reducing or eliminating the impact on adventuring mechanics; people should
not be picking their backgrounds in order to optimize skill bonuses.
Reduce the number of magic items, while making each item much more interesting. Instead of thousands of three-line statblocks, the 5E Adventurer's Vault should contain a couple hundred generic items, plus 50 to 100 artifacts. Artifacts would resemble 3E items of legacy. They would grow with the character, each artifact having multiple stunt powers available at different tiers, unlockable properties, and so forth.
The idea here is that artifacts take the place of the current weapon/armor/neck slot items as the core items that everybody is expected to have. Each character is expected to have, let's say, 1 artifact per tier; so you get your first in Heroic, your second in Paragon, and your third in Epic, plus a handful of generic magic items. Generic magic items round out your character; they include "plain-vanilla" magic weapons and armor, specialized utility items, and consumables.
Yes, this means you could find and affix the Hand of Vecna in the Heroic tier. Of course, you won't learn to wield its full power until Epic. But you do get to be the guy with the Hand of Vecna... with all that that entails. (Most artifacts would be much less world-specific, of course; they would be things like the sword Flametongue, or the Staff of the Magi, or the Holy Avenger. But it wouldn't be D&D without the Hand of Vecna.)
Incorporate RP elements in the form of skill challenge modifiers. Be sure to balance them against each other, not against non-RP mechanics. For instance, if you possess the Hand of Vecna, you might get 2 automatic successes in any skill challenge dealing with the followers of Vecna, but 2 automatic failures in any skill challenge dealing with servants of Lawful Good deities.
Since +X items are going away, of course, the DM does not
have to hand out that many artifacts. The game will be fairly understanding if you give out more or less; it won't throw the math off.
Recognize that some players like to play the fox and some like to play the hedgehog, and design accordingly (for those not familiar with it, I'm riffing on the saying that "the fox knows many things, the hedgehog knows one big thing"). Design some classes as fox classes, where you get a large number of powers, and other classes as hedgehog classes, where you get a small number of powers and an across-the-board bonus to compensate.
For instance:
Fighter (fox) vs. Barbarian (hedgehog)
Druid (fox) vs. Cleric (hedgehog)
Wizard (fox) vs. Sorceror (hedgehog)
Rogue (fox) vs. Ranger (hedgehog, at least in combat)
Warlord (fox) vs Paladin (hedgehog)
(I'm not wedded to that specific arrangement, incidentally. It's just showing one way the classes might be sorted out.)