It seems unlikely that GT300 will be joined by cheaper members simultaneously. Unless the machinations at 40nm crunch everything up. Given that 3 GPUs have just launched simultaneously, maybe something similar could be repeated with GT300.
Historically nVidia has always started on a new process with lower-end chips first, to 'test the waters'...
If these mobile 40 nm parts are the 'testing the waters'-phase, then GT300 is probably still a few months off (assuming it's 40 nm, and not 55 nm... but I think that's a safe assumption).
In that light I think there is room for some lower-end 40 nm desktop parts aswell.
But looking at the actual desktop product line from nVidia, I'm not sure where it would fit in... Their high-end has moved to 55 nm quite recently (January this year, I believe?), and shrinking to 40 nm so soon would probably make the 55 nm shrink a poor investment.
So the 9800/GTS250-range would be the most logical target for 40 nm... But... that product line is getting VERY long in the tooth. Do they really want to shrink that architecture yet again?
So the way I see it, putting 40 nm on the desktop at this point wouldn't be a very good investment. They'll probably want to wait a few months, then shrink GT200 to 40 nm, and replace the older G92-based product line with it.
But that all depends on how GT300 is going. Will they have a 40 nm GT200 as mainstream parts, with a GT300 high-end? Or will there be mainstream GT300 variations at launch? Or perhaps GT300 is more than just a few months off?