I'm hoping that someone with some experience with Windows 10 Subscription based licensing can assuage my concerns after some behaviour we've observed during initial testing.
It seems after assigning a user a Windows 10 subscription license, it will automatically license any device a user logs into, regardless of the state of the PC (e.g. KMS activated, etc.).
Our testing staff log into their own Azure AD devices successfully and automatically switch to subscription based activation as desired. There are some annoying caveats (the every 30 day check in and subsequent reversion to Windows 10 pro is annoying, but liveable), however it works mostly as desired.
But here's the problem - we have thousands of shared PCs in teaching spaces (University). These all remain on our campuses, happily activating against our internal KMS servers as required.
Now when a user who's been assigned a Windows 10 subscription license logs in, the KMS configuration is overwritten and the device is converted to subscription based licensing. The shared device then joins the list of 5 managed devices for that user, and is subjected to all the behaviour relating to Windows activation that comes with shared activation.
Additionally, our 10's of thousands of students don't have a subscription based license, so it's possible if no staff log into these shared devices, they can eventually revert to Windows 10 Pro and stuck in a weird state.
So, in essence, the technology is useless for shared spaces. I've had a support call with MS which resulted in reiteration of existing documentation and confusion over the use case.
MS Office 365 already has this issue resolved with Shared PC licensing; however, the design of Windows 10 subscription activation is fundamentally flawed in this regard from what I can tell.