DKMS is an awful user experience, it's an easy way to render a system unbootable. I hope Linus doesn't force existing users, like me, down that path. It's why I avoid zfs, however good it may be.
That said, I vaguely seem to recall that bcachefs ended up involving changes to other parts of the kernel to better support it; if that's true then DKMS is likely to be much more painful if not outright impossible. It's fine to compile one module (or even several) against a normal kernel, but the moment you have to patch parts of the "main" kernel it's gonna get messy.