But consider: ext4 was done entirely in tree, and btrfs was upstreamed much, much earlier and took a lot longer to stabilize.

So compared to historical precedent, we already upstreamed much later. e.g. we upstreamed long, long after we stopped making breaking changes in the on disk format (that was the point where btrfs removed the experimental label!)

If we're saying even that is too soon, then we're saying that bcachefs shouldn't have been upstreamed until it was perfect. But, no one was ever going to fund developing a filesystem from scratch all the way to completion and perfection completely out of tree. That's far too much uncertainty, and that kind of money simply isn't being thrown around in the Linux filesystem world.

Asking a filesystem to only be merged when it's completely done and perfect is saying "we want all the benefit and none of the pain", and it's just fundamentally unrealistic.

The whole point of Linux is community based development, and that's how I've been developing bcachefs. I don't have a big engineering team - but what I do have is a large community of people doing very good QA work that I work with closely, on a daily basis. People show up from anywhere with bugs, I ask them to join the IRC channel, and we start working together and it goes from there; a lot of people see us doing productive work and stick around and find ways to help out.

If that no longer works within the development model of the Linux kernel... oi vey.