It's getting down to the wire whether this shader cache will land for Mesa 17.0. The OpenGL on-disk shader cache is needed for better load times and more consistent performance in some newer Linux games that are heavy on GLSL shaders, such as Shadow of Mordor. This initial shader cache implementation though is just for Intel's i965 Mesa driver.
While this shader cache for Mesa has gone through many revisions and been available in patch form for months, it's not yet in Mesa Git for 17.0. It's not clear yet if it will make the deadline: the Mesa 17.0 feature freeze is this weekend, around 13 January. The Mesa shader cache hasn't merged yet since not all of the patches have been fully-reviewed by upstream developers.
While this is an important feature and puts Mesa one step closer to the features offered by the proprietary drivers, it just hasn't got enough reviews yet. Mesa release manager Emil Velikov mentioned this morning it would be noticeable to include it in Mesa 17.0, but first needs to get in the final reviews.
We'll see in the next day or two if the on-disk shader cache gets merged for Mesa 17.0. Mesa 17.0 is supposed to be officially released in February, but if the shader cache doesn't make it, the next opportunity to get it in a stable release would be Mesa 17.1 in May.
Also likely to still be merged for Mesa 17.0 is the Etnaviv Gallium3D driver, which has received reviews, and should hit Git within the next two days.