Intel's Ian Romanick laid out some release plans for upcoming Mesa releases in a new mailing list message. Ian's tentative schedule, which no other Mesa developers have objected to, puts monthly 8.0.x point releases out through August and to then have the Mesa 8.1 release happen in the middle of August. In particular, Ian is looking at releasing Mesa 8.1 on the 17th of August. Lately they have been putting out major releases about every six months, so it's not much of a surprise to see this late summer release for Mesa 8.1.
Following the August release of Mesa 8.1, 8.1.x point releases would come every month (pending worthwhile fixes landing) and to then do a Mesa 8.2 or 9.0 release on February 15th of 2013. Ian may release Mesa 8.2 as Mesa 9.0 if OpenGL 3.1 compliance is reached.
Originally there was some hope we would see OpenGL 3.1 in Mesa 8.1, at least for the Intel DRI driver, but it doesn't look that's going to happen. The open-source Intel driver can do GL Shading Language 1.40 in Mesa 8.1, but full GL3.1 support doesn't look like it will come. OpenGL 3.1 was ratified in 2009 by the Khronos Group and has been supported by the proprietary NVIDIA/AMD Linux drivers since then (along with all of the Windows drivers) but it will be about four years by the time Mesa has the support.
OpenGL 3.2 or any other newer version of this industry-standard graphics API isn't even being targeted for the Mesa 8.2/9.0 release in early 2013... We're already up to OpenGL 4.2 as the latest Khronos spec (ratified last August) and this year we still should see OpenGL 4.3 or perhaps even OpenGL 5.0. Unless there's significant investment by various vendor, it looks hopeless that Mesa will ever catch up to the upstream Khronos spec (and the proprietary drivers) in the foreseeable future. And the OpenGL compliance isn't the only Mesa shortcoming.
Jakob Bornecrantz, one of the Gallium3D/Mesa developers at VMware from the Tungsten Graphics days, did ask Ian, "Any chance we can do 3.2, or does it involve sudden cold fronts and aeronautical members of the suidae family? Being able to develop test apps on Linux and get the same functionality as on Mac is kinda cool."
Ian's response to Bornecrantz was "I have pretty much zero confidence that the remaining 3.2 features could be implemented and tested to a reasonable level of quality in that time frame. The experience with shipping OpenGL 3.0 earlier this year hasn't made me very enthusiastic about committing to aggressive ship dates."
As far as Mesa 8.1 even being stable, Ian added, "It will be a new release with a lot of new functionality. In this industry, people know what that means. :)"
As far as OpenGL 3.1 compliance in core Mesa goes, the GLSL 1.40 support isn't fully complete, there is not yet any uniform buffer object support, and the texture buffer objects needs GL3.1 enabling within the i965 driver. The best OpenGL 3.1 support continues to be in the Intel Mesa driver (after all, Intel OTC developers are the ones doing most of the support these days) with features like instanced drawing, buffer copying, rectangular textures, and signed normalized textures being implemented in that classic DRI driver. The R300 and R600 Gallium3D drivers do have some GL3.1 features while the Nouveau driver is lagging behind greater, at least according to the Git version of GL3.txt.
While it doesn't look like there will be full OpenGL 3.1 support for Mesa 8.1, at least there are other interesting changes building up for this next update.