I think this is especially true of the traditional D&D blogosphere. A few years ago, when Monsters & Manuals hit its 1000th entry, I put up a post bemoaning the decline of blogs. In hindsight, I shouldn't have been so hasty, because actually my own blog entered a bit of a "Silver Age" shortly after that that lasted a good two years, during which my readership exploded to levels never before experienced. It has gone down a bit since then, but that's mainly attributable to me posting less frequently and with less quality, I think, than previously (parenthood has given me a permanent -2 to my INT score; I hope it's not cumulative with each baby).
But it's indisputably the case that blogs aren't what they were, partly because the "stylistic and commercial underdoggery" has gone away, and partly because so much has been written and said that needed to be written and said that it feels as though we've run out of things to write about. There is always going to be call for more creative content (monsters, art, new rules, etc.) but any more writing about the principles of good play would probably now be flogging a dead horse. We've got 10 years of that behind us.
I think, though, that a few big undiscovered countries remain - enough, in fact, to provide plenty of grist for further elucidation and insight. For starters:
- Nobody has posted anything definitive yet about running underwater adventures/campaigns
- And for that matter nobody has posted anything definitive yet about running wilderness exploration adventures/campaigns either
More than that, though, while we have become very good at ploughing the furrow of "rogues exploring a sandbox in order to get rich", what we have only begun to scratch the surface of are different modes of play. Think of all the metaphorical internet ink that has been spilled on how to successfully run rogue-PC-oriented sandbox games, and consider that there is surely an equivalent amount of that ink to spill on how to effectively run games that have different sets of starting parameters. What, for instance, are best practices for games in which the PCs are "good guys"? What about best practices for games about spying or diplomacy? What about best practices for games in different eras - pseudo-Victorian period, pseudo-Ancient Greece, pseudo-WWI? What about games in which the PCs are defending an area from invaders? And so on.
What I think it boils down to is: we've said most of what we need to say about dungeons and hexcrawls. But there are more things in heaven and earth than that.