As of today Mesa now has full OpenGL 4.4 support (with 4.5 already done) for both AMD radeonsi and Intel (i965/gen8+). Mesa won't actually expose any higher than OpenGL 4.3 until Mesa (well, someone) pays up for the Conformance Tests.

Something I entirely missed when writing about Mesa and OpenGL, is that the open source Vulkan driver "radv" has been merged into Mesa.

The open source OpenGL driver AMD radeonsi is now extremely close to having full OpenGL 4.4 support, and OpenGL 4.5 is now complete.