I think a good bit depends on how they release it. If they release a core rules book and then sell the "modularity" in additional books, then I see a greater chance of people being unhappy. But what if they have the core assumption in the first few chapters and then the "modularity" tacked on in later chapters in the book.
Then a person buys one book and has what they need in one book. Want simple and rules light? Stick with the core chapters. Want a more complex system or a mix and match? Add in later chapters as needed to enhance your game.
I think physical presentation of this new D&D offering is going to have a rather large bearing on people's like and dislike of it.
Just look at the FR thread, there's posters in there saying they won't buy a product if they can't tear every mention of the Spellplague out of their books. One of the tough questions is do they put a whole bunch of modular elements in the first book or keep the modules actually separate.
Will people want to drop $75 on a big, initial offering with a bunch of stuff they don't want included or make the basic PHB $30 and sell the modules for $10 - $20 each?