Layer violations are fine if they give you value. ZFS is very layer "violating" as well. However, the layers are concepts put in place by humans to help, not God given laws of nature.

Agreed, and if you run on a microkernel, then pretty much everything is in userspace and any boundaries are those of, say, a capability system for security purposes. I still cannot wrap my head around the fact that we're adding ways to avoid the kernel network stack and other exceptions to the rule, while ignoring microkernels as the sorely needed feature for mainstream computing it is.

Yeah, Dominic Giampaolo. He works at Apple now and is heading its new file system efforts.

For years I though he was secretly writing a BeFS like replacement to HFS.

APFS seems less ambitious however.