Apparently, apple won't implement apfs for people on spinning rust so I can't get it on an iMac which made upgrading to high sierra easier. How did it go for people on macbooks?
Nor for RAID drives, whatever the substrate... except that by virtue of my participation in the beta programme, my Mac's RAID-0 array was converted before they decided to change track, and now after I wiped my system to restart anew I have literally no way of getting my system back to the initial state it was in.
You can convert those disks, they don’t do it automatically though. Diskutility has a convert option.
That's a dumb idea, the file system is designed for flash memory, not spinning disks.