They claimed they can make it run on a single core laptop without any kind of video acceleration. If this alone is true, its already a massive step. If they can do animations, then its a revolution. Which is why I'm very skeptic about this.
I wouldn't doubt it. The comanche series render the terrain almost the same way and it should run on dosbox on a single core laptop fine.
Other then the fact that it has about a billion times the number of things to keep track of in each area.
That actually doesn't matter as much. That only matters for memory consumption but if you use modern search algorithms you can render it fast.
The major flaw of voxels would be memory consumption. The more you increase the detail level, the more memory it will consume. On the other hand, polygon models are extremely tiny memory-wise, even the most complex ones, but the more polygons you have, the more processing power you need to compute them.
So voxels and polygons are fairly opposite processing-wise.
Notch rips this thing a new one, explaining how exactly it's impossible.
Except Notch is not a competent programmer. So whatever Notch rips, doesn't really gives it any less merit. Everything he has claimed in the past to be impossible to be done with minecraft is being done by modders. The only credit I give Notch is for sticking to his project.
Honestly, it's alright to be skeptical, but saying something is impossible because -you- (including me) cannot do it, is a sign of excess of skepticism. Specially if you don't believe it because Notch cannot it. If the world was determined by what Notch cannot do, maaaan, we'd be screwed. :B
But in all seriousness, there are a shitton of voxel/volumetric renders being used right now. Every day. They're used mostly in physics simulations, specially for fluids, and in MRI data.
Here:
http://en.wikipedia.org/wiki/Volume_rendering