We're trying to, yeah.

For this release specifically we wanted to have it out before the end of summer so that we can be ready to merge Andrew's migration work and any GSoC code and turn around another release quickly.

probably because 1.5 was the first release that didn't block master branch during the feature freeze period, so work targetting 1.6 was already progressing on master during the 1.5 bugfixing schedule.