You guys are all missing reality.
Without motion control, Nintendo would have opted for a graphically powerful system. If it'd have released around the same time as the Wii did, I'd expect it to have had graphics slightly more powerful than X360 but less powerful than PS3.
I'd also expect it to have a greater amount of flash memory in it, probably 2GB - still no hard drive. Online would have gotten more attention, but still lacked in comparison to XBL, and third-party support would have continued being extremely mediocre (although, the more hardcore multiplat titles would have actually made their way over).
And it'd have probably still launched at $250, effectively still selling well but not necessarily taking the #1 position. At the same time, though, the 360 and PS3 have seen bolstered sales, to a degree, thanks to the Wii - the videogame industry as a whole has been getting better sales thanks to the attention the Wii has gotten. As a result, neither of them would have quite the sales they have right now, either. Of course, their sales weren't affected anywhere near as much by the Wii's motion control + success, so they wouldn't have suffered as much... But, they WERE still slightly affected.
Since it'd have essentially been selling as a direct competitor to the others this time, and it'd have no special gimmicky concepts, Nintendo would likely have started emulating a lot more of what the competitors have been doing. As a result, online voice-chat would have already been released, a more organized and professional-looking user interface would have evolved, and the market would have not really begun the intense expansion it's facing right now.
I'd expect that the "Gamecube 2" would have probably ended up still taking first this generation, but by a very minor margin - the 360 would have been right on its heels with vastly superior North American sales and somewhat better European sales. In Japan, the GCN2 would've won out over the competition, particularly since the 360 would have still been a commercial failure there.
I'd put this generation's current sales as follows in the above scenario:
Nintendo Gamecube 2 - 13.50m
Sony Playstation 3 - 10.25m
Microsoft Xbox360 - 17.00m
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