My GPU is from 2007 or so and doesn't have a fan. It runs GNOME 3 perfectly fine. At that time it wasn't the fastest; I went for the cheapest fanless GPU that would still be supported by Linux.
That compositing requires more resources, yes, but IMO you're exaggerating on the resource requirements.
You still are talking about a x86 architecture with a discrete GPU.
It would be nice if it worked fast with no GPU at all like Gnome 2 did, so it can be used in Virtual machines, OSes with crappy drivers (*BSDs), weird architectures (MIPS, ARM, etc.)
Gnome 3 sacrificed all that compatibility to gain some nices graphics, I think it's not worth it.
That compositing requires more resources, yes, but IMO you're exaggerating on the resource requirements.