I’m sure it misses some part of what you’re looking for but there’s an old project on github called DrFTPD that does at least part of what you’re looking for, i

I’m sure it misses some part of what you’re looking for but there’s an old project on github called DrFTPD that does at least part of what you’re looking for, in a relatively archaic manner. It’s designed for a distributed FTPD across WAN links. It also has mirroring / striping, user accounts, etc. I’m sure you could find some tool to help it look local if needed.