Honestly the ability to do those major changes in place are pretty exciting and might be a draw towards BcacheFs for me. As long as it doesn't happen too often (with the experimental phase as an exception) it's really nice to be able to benefit from major features and improvements.
I really dislike the attitude some FS devs have that if you want some improvement made after you setup a system you should just reformat and restore from backup.
Sure a 5 hour metadata rewrite is disruptive, but it's nothing compared to a 5 day backup, reprovision, restore dance. The former can run over night on a weekend, the latter takes basically the entire work week. Therefore it won't get done until all the infrastructure is EOL, and replaced with something else 3-7 years down the line.
I really dislike the attitude some FS devs have that if you want some improvement made after you setup a system you should just reformat and restore from backup.
Sure a 5 hour metadata rewrite is disruptive, but it's nothing compared to a 5 day backup, reprovision, restore dance. The former can run over night on a weekend, the latter takes basically the entire work week. Therefore it won't get done until all the infrastructure is EOL, and replaced with something else 3-7 years down the line.