One could say wireless gaming isn't too feasible, but the Wave Bird seems to slap that idea silly. XBoX wireless controllers are 3rd party and cost nearly 80 dollars or so, and you can't use the port with Xbox Live because it takes up that spot. There was a 35 dollar one too, but its cheaply made.
PS2 I believe has no wireless controllers aside from something from Logitech, correct me if I'm wrong.
As far as the rumor of another wavebird is concerned, Nintendo mad a deal to from some company (Matsushia I believe) to use their 2.4 Ghz chips (rumble perhaps?) (Check the news archives) So who knows??
Wireless GBA? Like you said, 'bout time, all it needs to be is decently priced, OR heavly Advertised of its strengths outweigh the price. Since I got a Wavebird, I really never looked back, so just picture Wireless GBA!