Intel takes open-source software and Linux very seriously as shown through their Open-Source Technology Center (OTC) and various other initiatives. Intel's commitment has shown and most of Mesa's developments these days for new OpenGL extensions and other capabilities are done by paid Intel employees.
Earlier this year we received confirmation that Intel has 20~30 open-source Linux graphics driver employees and that they're still hiring more Linux developers. Since February when reporting the 20~30 count, there's only been more hires.
Now within the Phoronix Forums, "Kayden" of Intel's OTC team has written, "the Mesa development team at Intel has grown by nearly 10x over the last 3 years. So there is significant investment going on. It's always hard to find qualified people, and even then, at some point you hit the classic Fred Brooks problem where adding more people to a late project only makes it later."
In terms of Mesa being behind in OpenGL support where right now there's only OpenGL 3.2 support officially while the latest upstream OpenGL Khronos specification is 4.4, Kayden wrote, "The pace has picked up considerably, but so has the attention and importance. We're still on track to hit 3.3 by the end of the year, and working on 4.x features as well. If there are particular features people need sooner rather than later, we're open to that feedback."