There are some problems with modularity of rules:
1) an adventure module is published. On the back cover, they spend 44 lines of text telling you they use rule a but not b and module c for combat is required and the magic system the bad guys use is module a again, ad nauseum and they have no room to tell you what the cool adventure is. Inside, the adventure writers have to spend 16 extra pages of notes on "if you don't use this feature, replace it with that feature" stuff.
If writers force themselves not to do this (explaining the build) and instead write around such issues something pretty interesting might come out. If the writers instead of explaining that the hexcrawl rules of product X will be enforced and instead write the adventures so that the hexcrawl rules of product X can apply to the general description, if one choses to do so, but otherwise the general description stands as is.
Thinking of which; if the rules are designed in such a way that the rules burden becomes a player burden and the DM burden is words only, adventures can be written without any rule support at all. This is just an idea that I haven't thought through yet. But bear with me, example follows:
DM: You enter a room and see an orc standing in the middle of it.
Player1: Do I detect anything edible? I succeed in detecting.
Player2: Do I move first? I succeed in initiative.
Player3: I stumble and fall. (I failed my spider climb).
DM: You see a pie in the room. P2 you are free to act first.
As you can see the DM just adjudicates what happens based on what the players put in. The DM is above DCs and such and is only interested in hearing if the players think they succeed or not. By dumping the rules bit on the players each player can add any amount of rules to their own plate since anything you do will amount to a either a success or a failure, which the DM is free to make of what he wishes.
This must be the most interesting D&D thought I've had for weeks. I'll mull it over. Please feel free to add your own.