I unplugged all peripherals and rebooted: Nothing.
I decided to try and go in through linux to grab the latest clover and settings, and thought I'd throw the Sierra volume into gparted.
Something happened, and I needed to repair it with fsck.hfsplus command in linux.
Apparently, my drive needed "minor repairs", though First Aid in the usb installer I made couldn't find anything the last time I tried. I also tried deleting /System/Library/caches/com.apple.kextcache/* to see if that would wake the beast.
Anyway, that didn't help either - still the same issue.
Somewhere, I picked up on the idea that I could run the installer, and it *wouldn't* overwrite anything except system, so I'm currently sitting through an install.
However, I'm not holding out hope for a clean boot because my clover options still say "cancel hibernate wake" when I press the space bar on a boot option (which hasn't helped at all).
Will report back and let others know once it's over if it worked, or if I need to jump back and properly delete "/System" entirely and try installing again - that way, at least my home folder is preserved and I can get back to it.