Might be interesting to replace that FAT12 with something that supports more than 8.3, not just larger volumes - but yeah, that's going to be insanely hard and you'll have to change a lot of the underlying CP/M code, etc. as well as the GEMDOS side and certainly the apps too. FAT32 is likely going to be an insane effort because it's a hack where a file takes up as many 8.3 file entries on top of the original as it would take to store the name.
Oh well. But yeah, you'll likely want to create a for-loop that passes VIA addresses one by one for each of the 7 possible locations, trap on segfaults, and if you successfully read block 0xffffff and get proper block sizes from the drive instead of an error, you can make use of that drive. This probably can happen during the boot loader if you can grow it by a bit, or possibly as part of the BIOS when it is initialized.
Filter, yes, that perhaps too. The thing I don’t get is why there is a green ground wire, like others that have the ground embedded in it, that is clipped on both ends (the copper nubs at the ends), and the actual ground wire is soldered directly to the ground terminal of the power cable connector. Did someone mod this thing to just bypass the ring, or what happened here?