You can implement a single client NFSv3 server that provides stronger than expected (of NFSv3) guarantees and if you implement the "optional" companion protocols it should come closer to local filesystem semantics than most network filesystems. What would be neat about such a solution is that you can run the server either locally or remotely (same site, high bandwidth, low latency) and at the same time clients would have to a custom FUSE server or even worse load an (from the customer's point of view) experimental vendor kernel module. Upgrading from NFSv3 to NFSv4 would get you a bit closer to POSIX semantics, but of course it would still be NFS just not over a congested, jittery link to a shared server. Especially NFSv4 delegations could be a nice way to let the clients kernel buffer a lot of bursty async I/O locally. Just keep in mind how little POSIX really guarantees instead of assuming it will behave like ext4/XFS or even better ZFS on a laptop NVMe with two levels of power loss protection (big caps in the drive and the laptop battery).
I think this is exactly right, but there are lots of people who don't want to manage their own NFS servers -- that's who we're targeting with Regatta. Notably, I think that v4 delegations gets you close but not close enough to the performance that we're looking for. For example, you can't get a delegation for a directory (which means that you're still doing round trips for CREATE and UNLINK), which seems to be the case even with "nocto". But, I need to spend more time playing around with that.
