Commit 37502d2733c8ba8bc0d93e6f126534f23111fc3e added support of cache LVs by including dm-cache modules unconditionally.
Additional code is required to make this work with 'hostonly' for cache devices and for all underlying block devices.
This should be mostly identical to thin-pool handling.
I must have misunderstood how dracut modules work - seems the support is conditional after all.
Now we only need to remind anyone trying to use cache for root FS (among other things) to not forget to call `dracut -f` or will need a LiveCD...