We've seen this story before, and we know how it ends. Either the proprietary API fails and ends up as a footnote in history (glide). Or it closes off competition, and we get half-assed refreshes of the same technology for a few years (EAX), until the entire industry just gives up and goes another way.
The only people that should be cheering this on are AMD stockholders. This is a huge step back for gamers. At best it's a distraction for a few years, but it could get really ugly if it succeeds. You can call people crazy if you want, but we've seen this happen before, and the results speak for themselves.
Even if they don't stop developing for DX anytime soon, this could give AMD cards such a price/performance advantage, that they just won't be competitive. If that happens, and AMD no longer has NVIDIA lighting a fire under their ass, innovation and performance increases will slow to a crawl.