As mentioned in a child I definitely didn’t find it stable. It seemed to use masive amounts of CPU for unclear reasons and locked up a handful of times in my testing. When force-rebooting the filesystem was corrupted and seemed to continue to lose data after that point.
But that being said I think it may actually be good to merge it. It seems that there is lots of interest and the maintainers will be around to keep improving it. Getting it in the mainline (hopefully with some sort of “beta” label) will help it get the testing it needs. If the work is going to be done either way it seems best to be working in the main repo rather than keeping it separate and needing to continue handling migrations and merge conflicts. Look at BTRFS. It was known for data loss but now seems to be pretty stable with lots of eyes and lots of work.