There seems to be a lot of "begging the question" going on with this set. I think it's a pretty interesting model of designing 5 "mini-sets" and then wrapping them into one, but I think their explainations are a bit contrived, or at the very least, irrelevant.
For example, defining the worlds by "what they are not". So, for example, the Black world with Blue and Red doesn't have White or Green, the two colors of life, so th Black world is all about death and destruction. Wow, that's so much more interesting than just plain Black, which is about...death and destruction.
And the blue world...rules by wizards, that's simply ingenious. So original. I agree about the artifact thing, BTW...But I think their model of only 3 colors per world sort of did in typical artifacts, so if one of the groups realized that and felt that they could do something interesting with artifacts, then why not. That might end up being a pretty decent idea for the set. I'm just bothered by the flavor issues. Particularly when you have a "Artifact Creature - Human Wizard".
The other thing that has me wondering a bit is that each "world" was sort of built in a vacuum, but were the worlds built to have tension within itself? I get the impression that it's more like Ravinica, where each world was built to be a team against the other worlds. I'm just wondering how things work out if you don't have a foundation of conflict specifically within keywords. You could very easily end up with some balance issues, not based on power-level, but based on matchup. How do you insure a RPS environment between the 5 worlds?
It will probably be an interesting set based on an unusual experiement. We'll see.