Ian Romanick, the Intel Open-Source Technology Center developer that's been handling Mesa release management lately, is now talking about the Mesa 9.1 stable branch.
Ian wants to branch Mesa Git master on 25 January with the plan of then doing the Mesa 9.1 stable release on Friday, 22 February.
This release information can be found via this mailing list post. It looks like he's planning to do this next release as Mesa 9.1 and not Mesa 10.0.
The many Mesa 9.1 changes have already been talked about on Phoronix.