Continuity needs to work with multiple iCloud accounts
As it stands at the moment, Continuity (Handoff, Universal Clipboard, iPhone Cellular Calls, SMS/MMS messaging, Instant Hotspot, and Watch Auto Unlock) works, as it says in the instructions, only when "each device is signed in to iCloud with the same Apple ID."
However, and i'm sure I can't be alone in this, a household might have one central iMac with lots of other personal devices, each with it's own Apple ID.
For example, we have one iMac and it has an Apple ID. We have an iPad that shares the same account, so that's fab and Continuity works. BUT, my personal iPhone has an Apple ID that's mine, and my partner's has another Apple ID. So, that's 3 Apple IDs but only one device can work with Continuity.
That really doesn't make sense to me, and I do think that the functionality should be expanded so that I can register additional Apple IDs to work with Continuity.
Oh, by the way, the personal accounts are linked to the main Apple ID as Family Sharing members, so most of the admin for this is already there!
Thanks for listenening
iMac, macOS Sierra (10.12), iPhone 6, Apple Watch & iPad Air 2