I think what it needs most of all, then, is a decent licensing paradigm.
To clarify why I think this is the best way to meet everyone's needs:
Official material always, always sets an expectation in the minds of players. The DM is free to disallow official material but because this violates player expectations it can lead to disappointment, which in turn makes some DMs reluctant to do it. Thirdparty licensed material sets no such expectation precisely because it's not official.
With a continuous splat-book schedule, some players also develop a "gotta keep up with the Joneses" or "gotta catch 'em all" attitude, which can prove an impediment to new or casual players, who instead suffer from option-overload. Thirdparty licensed material is boundless and infinite: there's always going to be more books, articles, PDFs, en5iders, etc. So it's easier to ignore, and not feel any obligation to stay "current."
It can be harder to experiment in official material. People expect it to be balanced, playtested, and compatible with existing material -- not weird new ideas that throw major parts of the game all out of whack. Thirdparty licensed material is almost expected to throw the game all out of whack, and personally, I think it's at its best when it contains weird new ideas.
These are all subtle issues involving subconscious player expectations, and I'm sure some people will read this and think "sheesh, people should just get over it." But humans have an annoying tendency to not get over it. I think a good thirdparty licensing model would manage these expectations well, and satisfy both the people who want lots and lots of crunchy rules options
and the people who fear rules-bloat.