I wouldn't say linux just dropped support for it since it is the distro vendors that choose not to include it. I am sure if you wanted you will be able to get the source and compile a kernel module, but I do not understand why you would go through such pain for an obsolete technology, current file systems will work just as well on old hard disks.
Regarding your MFS question, I would not be able to answer as I have no experience using minix as such. Not that I know or did research on the origin of extfs, if what you say is true, that it is forked, I would imagine the original MFS has the same or similar caveats, and they surely updated the filesystem specs on newer editions to address the shortcomings.
Sorry I cannot be more helpful, but interesting question you posed none the less.