Last I heard there are no plans to do this.
If true that's a pity.
20 years ago, Apple cared about macOS as a Unix, they were interested in putting in features that developers and sysadmins wanted, like this.
Sadly, today's Apple has a rather different attitude towards that sort of thing
Re:ARM64 Linux Workstation
by fidgewidge on Saturday March 04, 2023 @05:09AM
(#35019724)
I think they're uninterested because they have a documented and supported userspace VFS API. The problem is, it's really designed for cloud drives and so deeply assumes a sync model. Works great for the intended use case, much better than Fuse but if you want to do something unusual, not so hot.
There’s a new FUSE implementation that uses this technique: https://github.com/macos-fuse-t/fuse-t
Worked without problems for sshfs when I tested it briefly.
It exists already - https://threedots.ovh/blog/2022/06/quick-look-at-user-mode-f... - it is just that Apple hasn’t made the API public, and (AFAIK) won’t give you the entitlements necessary to use it. But, both are issues Apple could fix relatively easily - if they wanted to - and here’s to hoping the fix is coming soon
However, there is an alternative that works right now - have your user-space filesystem process act as an NFS or SMB server, and mount that. From what I’ve heard - https://lists.nfs-ganesha.org/archives/list/[email protected]... - macOS even supports mounting NFS filesystems over Unix domain sockets, which has performance and security advantages over IP loopback