John Carmack's repsonse: "Re Euclideon, no chance of a game on current gen systems, but maybe several years from now. Production issues will be challenging." https://twitter.com/#!/ID_AA_Carmack/statuses/98127398683422...
I trust Carmack's response over pretty much anyone's in matters of rendering engines. The guy is a god of coding them.
That said, I also view his perspective in this field as tending towards unquestionable. He's always seemed to have had a pretty sparkling reputation as well as the obvious talent.