Awesome, thanks for the reply. Good to know this stuff is being considered. Sync is becoming critical to me, so I'm excited to see continued support.
I was thinking if I could remember another instance of the "Save" issue (other than an Office app) and iWork has a similar issue. It's a bit buried and few people probably run into this, but I'm trying to figure out my workflow for creating new documents and getting them to sync. This is what I did to see the issue in Numbers:
Create a new document
Tap the share button in the top right
Tap "Send a copy"
Tap "Numbers" format
This only shows apps that support opening .numbers files, so I tapped "Send to.." to open the iCloud Drive share sheet
Tap "Locations" then "Sync"
This shows the same empty Sync window as saving in Office. Clearly you could work around this in a number of ways, and as I said few people have probably ever encountered this.
Thanks for the great service and for quick support. While right now I'm just using Sync for my own personal and work files, I'm hoping to move my whole office over to using Sync instead of all the disparate cloud storage systems we currently use.