With NVIDIA's proprietary driver not interested in GBM for performance reasons and such while the open-source developers not being interested in the company's EGLStreams approach for Wayland compositors, a new and superior API is being pursued by both parties. That discussion made progress at last month's XDC2016 conference: see NVIDIA Presents Over GBM vs. EGLStreams, The Big Wayland Support Debate Continues and NVIDIA's Proposal For A New API Better Than GBM Has Already Made Some Progress.
Now that things have settled down post-XDC, James Jones of NVIDIA who has been leading this charge has been working on some fresh documentation and headers around this proposed memory/surface allocation API.
They are now working on this GitHub repository with trying to reach a consensus on different parts of this allocator API. If you're interested in the topic, check it out. For end-users, it will still likely be months before this new design is agreed to and hopefully when we'll see it begin to be supported by the different GPU drivers, Wayland compositors, and other possible clients.