While I'm far from running such a game at the moment, I'm looking to see if anyone likes the idea and has anything to suggest for it, and whether I should develop it further.
The setting concept is that a wizard made a wish, a wish that the world was like what was written in the book he was holding.
The result is a world where folks earn xp, take classes, and level up, from their own point of view. Similar to the goblins comic, where the goblins specifically chose their own class, and gained the powers from what they chose.
In this world, anyone who hasn't made a choice of class is lvl 0, but any intelligent being can earn xp and take class levels. Only, the catch is, this new set of rules for the world just happened, and when it did, everyone got set to lvl 0, including all those who used to be heroes and masters. So obviously, this is a time of great chaos, as many struggle to regain what they once were, or gain more than they ever dreamed of having. Power plays, politics, coups, people everywhere are living in chaos as they adjust to the new world.
Some good did come of it though, previously evil only being now have free will regarding alignment, anyone can gain power from willing followers, etc.
Unlike d20, xp is earned by overcoming challanges of any sort, whether combat or not. The more difficult the challange, the more xp earned. Many militaries and similar groups have established training grounds, to challange the soldiers so they can gain xp.
Unknown to most though, is that all the old ruins and more new dungeons, have all been created/revamped, to be challanges to those folks who dare tread inside, plus rewards at the end.
In a way, this setting brings certain meta elements into the world itself, but it is also about how those things might radically change how the world works, (ie. soldiers who used to rely on swords, now must consider, are swordmages the superior way to fight battles? Who wins, pure fighter or fighter/wizard?).
I would like to change some things from d20. No spellslots for example, spellpoints instead, or a will save vs fatigue type deal. Same with health.
Do what does everyone think of this? Would this be an awesome campaign to play?
This could be fun, but I'm not sure if it would make for a good longer term campaign. Being meta could be fun, but it could also also get old like a running gag that goes too long.
You could even have some more fun if you had each of the players make characters based on themselves (at least start with attributes similar to their own), as though the players were being brought into this RPG world, and let the players decided if they want their characters to try to get back to reality or stay in this RPG world. They could start as level 1 commoners and then pick better classes and level up. There may even be other real people that have been brought into the RPG world who want to get out or stay in. This could be a source of conflict if "in" or "out" is an all-or-none sort of thing. Some people want to rules kingdoms and keep this world and others want to get home and discard this world, and both are fighting each other.
I don't quite understand the changes you want to make to the d20 system, but I'm sure your players will let you know if the changes aren't working for them. Be sure to share your house rules in more detail if your players end up liking them.
Anyways, I think it is a fun idea that should be tried.
To be honest, I probably wouldn't use d20 at all.
As for running gag, I like to pervert expectations and stereotypes, in this case, I'd like to treat it somewhat seriously. Sure there'd be room for jokes around the table, but in the gameworld, I'd treat it seriously.
As for bringing myself into the world, not likely. I get frustrated with game systems being completely incapable of handling a character doing some of the things I've actually done. I find it best to avoid such frustrations.
Have you read Erfworld? It's sorta like this but for a strategy game. Should help with some ideas.