I don't believe that there is any particular reason for such HUGE firmware upgrade.
After all, firmware upgrades are supposed to address some bugs or any particular issues with the device and I haven't heard about any of such bugs or issues with the camera.
They sure could fix up video features they left out, although now with ML I guess we have some of them already and will soon have more. I don't think ML will be able to deliver crop mode video though and we will have to see whether it can fix AutoISO for stills or not.