For those that haven't been reading Phoronix the past few years, GLVND is the OpenGL Vendor Neutral Dispatch Library and is a NVIDIA-backed effort but with support from the upstream Mesa community for basically forming a new "Linux OpenGL ABI," as it's been referred to as over the years. Working to address the situation of different drivers competing for the libGL.so.1, and when installing NVIDIA/AMDGPU-PRO drivers currently, they clash with the current OpenGL library. This new 'Linux OpenGL ABI' takes care of it in simple terms by postfixing the driver's name to each supplied libGL so they can happily co-exist on the same file-system while the central (GLVND-supplied) libGL.so.1 effectively works as a dispatcher so applications/games end up using the right driver. It's roughly along the lines of how OpenCL and Vulkan drivers are implemented, but sadly it's taken many years to improve the situation for OpenGL drivers on Linux.
Last month was the planned Fedora 25 update to enable GLVND in Mesa. Mesa has supported GLVND for a while and the NVIDIA proprietary driver has also supported GLVND for a few releases too.
But pushing the GLVND-enabled Mesa down as a F25 update has been causing problems for a minority of users. The biggest negative impact for users is that landing the GLVND-enabled Mesa had broke the Sway compositor, to which Hans has apologized for not correcting first but later took care of the situation. The issue has since been fixed for Sway and there's also a fix now upstream too. The other known problem with the update was that landing GLVND support had broke some Steam games, but that issue has also been resolved.
Why it came down though as a update to Fedora 25 with not making the original Fedora 25 debut and not delaying it to Fedora 26 is that it was a "promised feature" for Fedora 25 and that "from a technical [point of view] it is ready," according to Hans de Goede.
Some have argued that the GLVND enabling should have gone through the traditional Fedora change proposal process, should have waited for Fedora 26, or similar.
The Fedora Engineering and Steering Committee (FESCo) got involved in the situation and on Friday ordered that the update be kept in F25's update-testing until their next meeting when they will decide if this update be re-allowed into Fedora 25 or if it must wait until Fedora 26. That's what this very active devel thread has been about the past few days for those looking to read a range of comments on the matter or wanting to add your two cents to the discussion.