In principle, I agree absolutely. But the Geforce 4 works. AGP8X is entirely correctly specified, and will be totally functional and compatible. This cannot be said for DDR400. It's just not ready. That alone should put the brakes on right there. (not even considering whether people will actually buy it or not)
It costs $138 (on sale!), and will be maybe 2% faster than PC2100. Oh, and by the way, you can't use more than one, perhaps two, of them in a system without it becoming unstable, and having to drop back to PC2100 anyway.