Wow, AMD, very naughty...... locking out Nvidia, asking their Gaming Evolved partners to do absolutely nothing to help Nvidia..... oh wait. Nope.
Rroff, why would the market get fragmented if Nvidia got their own API, everyone would just have a AMD and Nvidia rendering path. AS it stands we can now have Mantle or DX, in the future we could just have Mantle or Nvidia... still two API's. AMD and Nvidia users get full value for what they spend, dev's get to push the boundaries with more performance at any given time and to get creative with what they can do without spending ages working around DX limitations. Likewise AMD/Nvidia can do what they want with hardware and adding new features because they don't have to work towards a future standard DX set of features, they can diverge and add what they want without it also having to be Nvidia compatible.
EDIT:- actually as it stands DIce have been working on Mantle, DX and Nvidia extensions, so removing DX and having a full Nvidia API would reduce the amount of work they need to do... well long term, we'll need DX support for current/previous gen cards, but it's something that can be phased out in a couple of years. Like I said previously we need a big group of game dev's to sit down, commit to wanting low level API's and get AMD/Nvidia to hash out an agreement to not block support for the other with any games they work on, with the threat that game dev's will pull support for either company that trys to block the other.
DX needs to die, low level API makes all the sense in the world.