I think the issue with any new physical filesystem, is even if it becomes mature, fully upstream as part of the mainline Linux kernel, and supported out-of-the-box by all the major distributions - still a lot of people are just never going to use it, because there is so much competition in that space (ext4, XFS, btrfs, etc), people are understandably quite conservative (fear of data loss due to bugs), and the fear that a less popular filesystem may end up being abandoned if something unexpected happens to its primary developer (see e.g. ReiserFS)
By contrast, improvements in performance of FUSE, L4-style IPC, could be much more widely beneficial-both for developers of new physical filesystems (by making possible in-user space implementations where they can iterate faster, get better API/ABI stability, easier adoption by end-users), but also for developers of numerous other pieces of software too
Of course, you personally are going to scratch the itch you want to scratch. But in terms of what’s most beneficial for the Linux ecosystem as a whole, I think FUSE improvements and L4-style IPC would deliver the most benefit per unit of effort
I agree about the benefit they'd offer, but the thing is - I already have a todo list that extents out to 2030, and FUSE is going to take a lot of work before it gets there: probably years, because it's going to be done incrementally on top of a big hodgepog instead of being done right by someone willing to invest the time to get it right.
We've had someone show up claiming "I'm going to do FUSE right!" and it never happened, so - the incremental approach is probably best here. But it's going to take awhile.
By contrast, improvements in performance of FUSE, L4-style IPC, could be much more widely beneficial-both for developers of new physical filesystems (by making possible in-user space implementations where they can iterate faster, get better API/ABI stability, easier adoption by end-users), but also for developers of numerous other pieces of software too
Of course, you personally are going to scratch the itch you want to scratch. But in terms of what’s most beneficial for the Linux ecosystem as a whole, I think FUSE improvements and L4-style IPC would deliver the most benefit per unit of effort