Simple, yet smart!
What it did support was all the Oric drives (if I remember correctly), from Microdisk, to Telestrat and Jasmin. He tested that, I think. I have played infocom games with Cumulus and my Oric, and other people did the same using a Microdisc clone and floppies. I was never able to test the latter, because of the difficulties to write floppies (need to get an old laptop, boot in MSDOS from disk, work from there with no USB nor networking... a pain).
No filesystem support, I'm afraid, so a bit ahead of reading/writing files. But surely a first step towards an OS which could support FAT disks.
Now the thing is that most PCs don't have a floppy drive, so even with that option, supporting FAT disks is less and less interesting. Much much better would be support all kinds of FAT and SD cards on cumulus
