I say good on them. Kernel is ABOUT 3months (technically isnt it usually 8 weeks? 7rc's and 1 week of merging?), firefox is about 3months if I'm remembering correctly, KDE will be on 3months now, MESA is on 3month cycles. Fast moving distros will love it, and slow moving distros dont have to change their plans since every 6 months will still be a new version-- now it will just be jumping from 5.0 to 5.2 then 5.4 every release, instead of 5.0 then 5.1 then 5.2 every release.
Its better for developers since there's no rush to meet a merge window (if you miss it, oh well, 2 months of stabilization for you then you try again next release-- not 5 months of stabilization) and its better for users since if developers aren't rushed to meet a merge-window then the odds of half-finished code being shipped as stable is less likely.
Short time release with only what is backed, seems to be a good development model for OSS softwares. Chrome started now all follows. I think this is good and should be spread more, do a quick release and only add features when they are done, not every release have to be ground backing.