i think that the emu scene kinda works in a pattern. with the first generation of the emu scene, the people were focused on emulating their favorite systems, the ones they grew up with. So the NES, SNES, Master System, and Genesis were all being developed in the mid 90s. Then after those were pretty much perfected, there was a pause so to speak in development. The programmers had accomplished what they wanted, emulation of their childhood systems. Then, late 90s, early 2000s, it jump-started again, but with the N64 and PSone at the heart of development. Why? Because the people who grew up with those were old enough to begin programming, and emulating their childhood systems. So, as we finish up those, there will again be a down-time for the emulation community. That's not to say that emulation of the newer systems will not continue to be developed in the mean time. It's just that the programmers are probably less enthusiastic about programming things they dont have significant memories of. So, yes DS, PSP, Gamecube, PS2, and XBOX emulation is being done, but not with the same speed and excitement. Just give it time, and then the youth of the late 90s, early 2000s will be ready to begin programming, and emulation of Sixth-Generation systems will refuel intrest in emulation. I think it works kinda like this:
Generation of Gamers ----5 years later----> That Generation of Gamers Grows Up, and an explosion of Development for those Systems is Seen ----2-3 Years Later----> All the bugs are worked out of those Systems, and a slow in the Development of Emulators occurs ----2-3 Years Later---->
A New Generation of Gamers are between the ages of 16-20 and are ready to Start the cycle again
However, this is just my hypothesis, and seeing as I wasn't around during some of these times I only have the knowledge my good friend google can provide me with. ^_^ Sorry if I sound like a n00b, it's just my way of viewing things.