I got the feeling, that the current API generation is getting more in the direction of a plattform dependent, partership-only programs:
- PS4: sony API closed/NDA
- Mantle: AMD only, no public API yet
- Metal: ?
- DX12: not released yet, most likely only known to certain devs.
n.b games consoles have always had low level GPU APIs
PS4/Xbone/WiiU/PS3/360/Wii/Vita/3DS: all unique closed/NDA APIs.
Mantle / DX12: in private beta.
Metal: available for iOS8 development.
D3D12 and GLNext will of course be cross-vendor.
Rumour has it that D3D12 will run on all hardware that D3D11 runs on, using the same feature-level mechanism -- i.e. from SM2/D3D9/GL2 era to the cutting edge.
Hopfully GLNext contains a similar feature level mechanism; I personally find feature levels a much, much more developer friendly alternative over classig GL's extension spaghetti...
Mantle is currently AMD only due it still being in development, but is specified in a cross-vendor way... but my bet is that GLNext will be a replacement for it.
It seems to only exist as a huge threat against Khronos -- make GLNext, or we will replace you ourselves.