I don't think the problem is that console gamers wouldn't be interested in a game like Eternity or that console gamers and PC gamers are completely disjoint sets, but that it's not necessarily a game that most people would want to play on a console.
I do some console gaming and I do some PC gaming. I enjoy both. Would I be interested in playing a game like Eternity on a console? Not a chance! And while I realize that my preferences aren't necessarily representative of the community as a whole, I wouldn't be at all suprised to find out that there is not really much of a market for mouse + keyboard, party-based, RT, isometric RPGs on consoles. (Even if many console gamers also enjoy playing this sort of game.)
That said, if people do want to play this on their consoles and Obsidian wants to try to make a port... sure, go for it! But I agree, that I would hope that that's something they work on after the PC version has already been released.