I really hope Linux can get a modern FS into common usage (as in default FS for most distros). After more than a decade ZFS and BTRFS didn't go anywhere. Something that's just there as a default, is stable, performs decently (at least on ext4 level) and brings modern features like snapshots. Bcachefs seems to have a decent shot.
What I'd like to see even more though would be a switch from the existing posix based filesystem APIs to a transaction based system. It is way too complicated to do filesystem operations that are not prone to data corruption should there be any issues.
Btrfs is the default on a few systems already like Fedora, suse, Garuda, easynas, rockstor, and some others. It's not the default in Ubuntu and Debian, but I wouldn't say it didn't go anywhere either.
I'm using BTRfs on Fedora (by default install) and it's been great over the last year.
The only thing to be aware of is to disable CoW/Hashing on database stores or streaming download folders. Otherwise it'll rehash each file update, which isn't needed.
I've been running it on my NAS-slash-homeserver for... 5 or 6 years now, I think. Root on a single SSD, data on a few HDDs in RAID1. It's been great so far. My desktops are all btrfs too, and the integration between OpenSUSE's package manager and btrfs snapshots has been useful more than once.
It isn't, and the problem is not in "hashing files" (or blocks for that matter). Checksum calculation is very cheap, especially if you use default settings (which prefer simple & fast checksum functions like crc32/xxhash instead of strong cryptographic functions like sha256/blake2 that can be enabled manually).
The real issue is that modifying large files on a COW filesystem causes it to spread that file's guts all over the disk (i.e. fragmentation), and results in serious performance loss over time.
For some reason that doesn't happen nearly as much on ZFS and it's totally fine for VM and database workloads.
What I'd like to see even more though would be a switch from the existing posix based filesystem APIs to a transaction based system. It is way too complicated to do filesystem operations that are not prone to data corruption should there be any issues.