The "core" of the game is 'Role a die. If it's higher than a certain number, you succeed, if it's lower, you did not'.
Everything else is a mod to that core.
(Any if you want to identify 'mod' as module or modifier... either works.)
I think the point may be missing that Different rules does not mean different options.
The game will hve the same basic rules. A basic player probably will have average skills and abilities.
I Feats and special abilities are going to be equal. Special abilities only deal with the character actual class. Feats may be in subclasses. PLayers will probably have the option to pick their actual special ability or choose a feat (like a barbarian ragee etc).
Spells will probably be auto assigned or have limited choices per level.
Race won't be an option, it's been in every addition and i'm sure was an oversight. But it will be the basics.
Miniature combat can be an option. But the rules will be there for distance and feet.
Combat maneuvers will probably be basic and be more ability driven.
Skills will be bonuses to ability score, possibly from feat choices. I think special abilities will give bonuses to ability scores automatically. Because you can swap these out, there is the "balance" in the two or three types of characters.
The super advanced book will have other races, and all kinds of zaniness for hte hardcore fan. I expect the math to be looser and possibly these classes will be weaker in mathmatical build.