I am maybe having similar problem with my laptop unable to boot Sabayon.
It was week 47 huge (433 updates) upgrade, which somehow broke my Sabayon.
After upgrade the booting ended up with black screen. Not even a blinking cursor at the top of left corner of the screen. So I could not get to terminal with Ctrl+Alt+F1 keypress.
When I select Sabayon-recovery X86_64-3.11.0-Sabayon
from grub I end up to a screen, which suggest that there is something wrong with LVM. "mdadm: No arrays found in config file or automatically...
I have no RAID system, just basic lvm partitioning with root, home and swap partitions on a SSD drive
See screenshot below.https://www.dropbox.com/s/gtl81y6jj0p8617/Sabayon_boot_failure.JPG
After I give the root password I get to the terminal. In terminal command: equo update gives an error "invalid file system encoding ANSI_X3.4-1968, must be UTF-8....
Filesystem seems to be read only and I can't therefore edit much of the files.
I have encountered this same problem atleast two times before about a year ago in month apart. At that time reinstallation was the solution but I am kind of tired doing that and would like to learn to fix this thing. And there are two other Sabayon installations waiting for those 433 updated packages to be installed. Sorry that I could not get the picture linked from my dropbox showing correctly.