I think that IGN's probably full of crap (as usual).
Kuju is apparently owned by Nintnedo, and is supposedly making some sort of GameCube-exclusive product. And they apparently recently signed up to do something with Konami.
But if this Kuju executive says "Castlevania to GameCube!!" on a message board, is he announcing a game, or just saying what he wants (like Nintendo saying "Mario for President!!"). It's obvious that people at Kuju probably like Konami, and Nintendo, as they've hooked themselves up with both of them, apparently.
So yeah, if it's true, it's good news. But I'm quick to believe that IGN is full of crap. But I also know that they're in a good position, and are often privy to details that the rest of us don't get to know.
As for my thoughts on this potential Castlevania, I hope it's a remake of SotN, not LoI. Like how MGS:TTS was a remake of MGS, not MGS2.
Either that, or something all-new. I really don't care if it's not "made by Igarashi", as Konami seems to have severely burned their credibility with that stuff. "Castlevania 64 sucked. But that's because I didn't make it. So I'm gonna wipe it from the 'official Castlevania history'. And Castlevania Legends too. Because it let you play as a girl. Boys don't want to play as girls. They want 'cool' heroes. Not girls. So Lament of Innocence is going to be the first 'real' 3D Castlevania, and it's also the 'real' origin of Castlevania." Sorry Iga, but when you say stuff like that, your game has to actually be better than the ones you're stepping on.