I don't think it'll be as big an issue as some people make it out to be. Microsoft is banking a fair amount on Natal, and will want to be sure that it's done right. (Patching hardware is much harder than software.) They are working on the lag issue, as shown from the 2 different demos of it, in where the second one has considerably less lag. However, here's what people don't consider- if the lag time is known, it can be compensated for. If you know that Natal can handle only 30 FPS (though I suspect this is not yet in stone), then adjust your input response window back 0.015 seconds. (This time is for half a frame, to catch whether you either do it right at the capture, or right after.)
The thing that people seem to forget, is that everything has lag. The estimated lag on a wireless controller is about 6 ms, or 0.006 seconds. If, as I suspect, Natal comes back at 60 FPS support, this pushes the median delay time back to 0.0075, which, really, isn't that much worse than a standard controller. (The human eye can not perceive a 1.5 ms difference.)
In the end, I do think that both Natal and Sony's thing will see some Wii ports, Sony moreso due to the similarity of input. But the removal of the controller as a form of tethering I think will cause some different things to be made for Natal. Of course, we won't know any of this for certain until they release. Being honest, I'm intrigued by Natal. I'd like to see it do well. And I do think that the final product won't have severe lag problems.
-dunno001
-On a quest for the truly perfect game; I don't think it exists...