Hi. My 2 cents on the matter, related to March update on RPI2:
After update, it would only boot into a limited console with busybox, could mount the SDCard partitions but that was all. I haven’t had enough time to dig more about how to boot from there. After many restarts and modifications to cmdline.txt and overwritten kernels, finally the boot partition gave up and couldn’t be mounted anymore. So I proceeded with a fresh install on another sdcard and updated OSMC without any hassle. Then I formatted the boot partition on the old sdcard and copied the content over from the new install. And then, magically, the device booted perfectly from the old sdcard. I was happy because I hadn’t made a backup in a long time.
Don’t know about other situations with RPi devices and the March update, but in my case that’s what really worked. Probably there is something wrong with the sdcard anyway, but I will replace it rapidly. Hope this helps somebody.