That should be a completely trivial for bcachefs to support, it'll mostly just be a matter of finding or writing the tests.
If you or others can get it done I'm absolutely starting to use bcachefs the month after. I do need fast storage servers in my home office.
As for ZFS, I'll be buying some extra drives later this year and will make use of direct_io so I can use another NVMe spare for faster access.
When I can spend some $3000 or so I'll absolutely buy several 20 TB drives and just nail the whole thing -- and will use ZFS -- but for now the several spare HDDs that I want dedicated to my data are set up exactly as you mentioned: root vdevs with no redundancy. ZFS is mostly handling it fine even though the drives have vastly different speeds (and one of them is actually an SSD).
So yep ZFS can still do quite a lot, it's just still not flexible enough in a manner that f.ex. bcachefs is. But the latter is still missing important features so I am sticking with ZFS for a while still.
Hope that's coming this year. I have a bunch of old HDDs and SSDs and I could very easily assemble a spare storage server with about 4TB capacity. Already tested bcachefs with most of the drives and it performed very well.
Also lack of ability to reconstruct seems like another worrying omission.