From Japan with Foreboding

Lucky Star (らき☆すた, Raki☆Suta)
Anime adaptation of the Lucky Star yonkoma

People who enjoy their manga via translation are often incognizant of the very specific conditions which nurture the stories they read: Most of them have actually been around for some time before being exported to other countries. The result of reading what is essentially a backlog of material is that certain things might be slightly passe by the time they leave Japan. For example, while the traditional long-form serial is far from dead, it may have already peaked in Japan. Well-known scholar Frederik L. Schodt points to the changing trends in reading and demographic patterns that are having a significant effect on manga:
The big problem in Japan is that the bubble in the industry has definitely burst for both anime and manga. I think it's probably worse than many of the official statistics reveal. I was in Tokyo in May - and I go to Tokyo every year to watch trends - and the thing that drove the point home to me is that on the train, almost no one is reading manga. That's a huge, huge change from ten years ago, huge. On top of that, you have a new era in Japan where there's a declining population of young people, which is still the main readership and market for manga and anime. So publishers and producers of shows are confronting this very stark reality that fewer people are buying their products, and there are fewer people to buy their products. It's not only that they are buying less, but that there are fewer people to buy them! So no one knows what's going to happen yet.
Which is reinforced by Jason Thompson:
But for all their cultural clout, weekly manga, like newspaper strips and network television, is a fading medium. Except for Weekly Comic Bunch (which skews towards an aging readership anyway), all the existing weekly magazines in Japan are at least 20 years old; recent attempts like Comic Gumbo have been failures. Publishing a weekly manga magazine requires tremendous resources, and with the fragmentation of media, perhaps the generalist audience required to sustain these massive magazines is dwindling. Oddly, there are no weekly shojo manga magazines (although there are several biweekly ones), possibly a sign of shojo's smaller economic footprint; a few weekly shojo magazines were published in the 1960s but never caught on.
But on the other hand, this benefits yonkoma in much the same way that many American webcomics are gag strips that take advantage of the internet:
Yonkoma manga is easy to make, easy to read, and—surprisingly considering its low profile in the U.S.—very successful. While other manga magazines' circulations dwindle, yonkoma manga is the fastest growing area of the manga industry. Four-panel series such as Lucky Star are increasingly being adapted into animation and merchandise. There are many magazines devoted solely to four-panel manga. Online and cellphone manga is overwhelmingly four-panel-oriented, as it's the easiest type of manga to read on mobile devices, and some yonkoma webcomics, such as Hidekaz Himaruya's Hetalia Axis Powers, have even become hits and made it into the big time.
Minami-ke (みなみけ?, lit. The Minami Family)
Anime adaptation of the Minami-ke yonkoma

What's the connection between the World Wide Web, Japan's aging population, and the growing fetish for kawaii schoolgirls? Is the nostalgic longing for fatherhood as youth and childhood become a more and more prized commodity really partly to blame? Is there perhaps a general cultural malaise at work here?

One thing for certain is that as Japan changes, so will the manga industry. A larger trend that neither writer mentions is that Japan as a nation might be developing a less American-centric view of the world even as Japanese publishers continue to sell to the American market. What kind of manga are going to be produced under the influence of these trends within the coming decades?