Regarding what needs to be done for a beta, Titi said yesterday that it would be nice to take another hard look at performance (but since it's a beta, this could be postponed, too). Regarding performance, he's mostly thinking about whether or not to enable the (currently disabled) cache we used to have in 3.6.0.3.
Personally I'd like all non-[tagged] bugs to be investigated and commented on (if only "not enough info, won't fix"), but this, too, could be postponed. It could be nice to create the betas on the new build infrastructure, though (to setup and test run the automation involved), also as a test run for (possibly) fully automated builds for the stable release, but this would most likely take more time than doing it the classical way.