Eternal Darkness does not need a sequel. Really. (I know, Dyack himself thought about it, and there is even a reference in the game, but is not necessary and would probably sold not that well).
That game, in N64, would have been remembered as one of its must-have in every list. Appearing in Gamecube made possible to have FMVs (very blurry, by actual standards, btw) and better graphics in general. But damaged a lot its long-standing memory in the general public mind (caused by the machine failure in the market). I doubt it sold better in GC than it could have sold in N64, even in 2001.
Great game, anyways.