Mesa moving forward will now use a YEAR.RELEASE-NUMBER-OF-THAT-YEAR scheme to signify their releases. Mesa 17.0 is due out in February as what was known as Mesa 13.1, then comes 17.1, 17.2, 17.3, and 17.4 if sticking to the existing quarterly release cadence. Mesa 18.0 will then kick things off in 2018.
Mesa 17.0.1 will then be the first stable point release to Mesa 17.0 and continue as 17.0.x for the point releases / minor updates.
Mesa 17.0 will be officially released in February with a grand number of changes from many RADV/ANV Vulkan driver improvements, OpenGL 4.5 for RadeonSI, in effect Nouveau NVC0 OpenGL 4.5 but not yet advertised as such, performance improvements, and much more as we've been covering in dozens of articles over its development period since Mesa 13.0.
The motivation for changing the versioning scheme as Mesa traditionally only ever bumped its major version number when reaching a major OpenGL extension level. But with Mesa now at OpenGL 4.5 compliance and no big OpenGL updates expected again, or at least for a long time, they needed to shift their versioning focus. Major Vulkan updates aren't expected to be rapid either, so moving to a year-focused versioning scheme has been their focus.