Ok, fair. We have completely different usage scenarios, and I admit I had overlooked this feature.
Speaking from the shoes of a designer working with multiple displays and I/O means, High Sierra (and the new MBP) have offered me nothing but setbacks.
It's not been all fair sailing. An unexpected snag is that for people like us with 128GB SSD laptops and 2TB iCloud storage, Apple provides no simple way to create a local backup of all files on iCloud. Time Machine will not backup iCloud files that are not on local storage - Apple confirmed this in a chat with Apple online tech support.
I have a large Time Capsule right here and several MacBook Airs that spend 10 hours a day connected to unlimited high-speed internet, but oh no, Apple won't make that possible. Apple's recommended solution is to buy another Mac, eg a mac mini, plug in a large HDD, and use that as a 'download all iCloud files to this computer' solution. I find that a bit unreasonable.
I've just built a cheap hackintosh (for other reasons), & will install a 4TB HDD for iCloud / TM. Seems all files will have to be stored twice - once as 'local storage' sync, and again as a Time Machine archive. (but 4TB is enough for now). I don't even know if OSX will maintain a local iCloud sync for users that are logged in but not currently active.
UPDATE: Now the hackintosh is in demand for the Windows 10 side, so I may need to run OSX in a VM on Win10 just for maintaining a local copy of iCloud Family Storage files. If it turns out OSX can't keep iCloud files for all logged in users synced at once, then I'll have to run multiple OSX VMs, one for each iCloud user. Utterly ridiculous but there you go.
Thankfully APFS makes it easy to allocate multiple overlapping partitions on a HDD so I can freely assign each VM its own 2TB APFS HDD partition for file storage, and have the total disk space used be equal to only the actual data stored.
