`ssh://pi@raspberrypi.local:raspberry` with "while true; do ls /dev/ | grep ^sd | xargs mount; done" in rc.local, running outdated 10 years old Linux Kernel booting from ROM with write enable pin tied to ground, is all that's needed. There's probably sshfs for everything so protocol support for dozen things isn't a must.

I mean, I have one for handling an HDD with busted power circuit that cause system resets at regular intervals(likely brush sparks from a power steering motor went back up through USB and killed it). It's almost wrong that there isn't a pre-made solution for this.