The only reason I could see why the ARB might consider making a third try for a new API (and again: they've tried it twice before) is because graphics cards aren't getting that many truly new features that require API extension.
DX11.1 hardware features are... scant:
- Shader tracing and compiler enhancements: Not a hardware feature. Not really.
- Direct3D device sharing: Not a hardware feature.
- Check support of new Direct3D 11.1 features and formats: Not a hardware feature.
- Create larger constant buffers than a shader can access: Welcome to the party, D3D; glad you could make it
- Use logical operations in a render target: Ditto.
- Force the sample count to create a rasterizer state: Ditto.
- Process video resources with shaders: Not a hardware feature, per-se.
- Extended support for shared Texture2D resources: Not a hardware feature.
- Change subresources with new copy options: Not a hardware feature.
- Discard resources and resource views: Not a hardware feature.
- Support a larger number of UAVs: Hardware feature yes, but only because D3D doesn't provide a query and a flexible count of these...
- Bind a subrange of a constant buffer to a shader: Welcome to the party, D3D; glad you could make it
- Retrieve the subrange of a constant buffer that is bound to a shader: Ditto.
- Clear all or part of a resource view: It took you that long?
- Map SRVs of dynamic buffers with NO_OVERWRITE: Welcome to the party, D3D; glad you could make it
- Use UAVs at every pipeline stage: Welcome to the party, D3D; glad you could make it
Most of these have little to do with actual hardware. Basically, since D3D11, standardized cross-vendor hardware features have been fairly few and far between. Sure, we've got AMD pushing virtual texturing. NVIDIA's pushing "bindless" textures. Other than that? No.
One of the cited reasons to abandon Longs Peak was that it was taking too long, that OpenGL wasn't being responsive to new hardware. There isn't any right now. Or at least, not much that's cross-vendor.
Again, I remind you: Do not get your hopes up! This will not happen, no matter how much you want it. The sooner you accept this, the better.