Been following Cyril's tweets about DX12 (thanks for the retweets Scott) and it's looking like this really is a release just to counter Mantle. So far they say they will support everything Microsoft from Xbox One, PCs, to phones. That last part seems to be something new but worthwhile to help people easily port from PCs to phones (good for Indie developers.) Then we see that AMD and Intel claim their current products will support DX12 at release time. I would assume that Nvidia will also do the same. That suggests that we aren't going to get anything special in DX12 that requires new hardware else AMD and Intel couldn't fully support the DX12 API at release time.
So it seems that AMD/Valve really did get Microsoft to move and address many of the issues that they and many developers have with the current Direct X. This seems like a good thing for all of us.