Bcachefs sure looks interesting.
Like many others I am limited to random collection of heterogeneous storage purchased pre AI - some of which I would have otherwise declared ewaste 
Being able to set redundancy at a directory level would let me simplify and utilise more of my storage.
Used ZFS in the 2000s, and btrfs recently, but to be honest aside from check summing of data I didn’t find it much of a jump over the old LVM / dm / md / (xfs|reiser|ext*) possibilities.
I think I’ll switch over to bcachefs for nas/san/backup storage management duty 