They need a basic remote API and SKD first. Now we have that anyone can implement these local daemons/translation layers if they want to. This is still early days.

They could at least have implemented a shell

They do have an interactive shells:

You can also run interactive shell. Just type ./proton-drive and then the commands directly.

Though the commands are not the same as Linux equivalents that is IMO not a big concern. Similar things like AWS S3, or even ftp also don't have the exact same commands. It is really a trivial thing to learn how it works.

And again, anyone is free to build on this now if they want to.

I would not be surprised to see a fuse fs popup at somepoint around this.