siri: meh
Universal clipboard: cool idea but not in my usage routine.
PIP: cool feature but on a 13 inch screen this is not so practical.
Disk space management: more iCloud storage needed.
Exactly. If High Sierra takes the under the hood changes further I say great, bring it on. In my case, I will probably wait for 10.13.3 or so before I update my computers. Sierra has been trouble free for me. So what if I don't use all the features of Sierra, not like it cost me anything.
I just recently started using PiP and I even wrote a post on how useful it is. I’m sure 3rd party browsers do this as well, but it’s really fluid and functional in Safari.