Starting with 20H1, officials said, "We've tightened access to Cortana so that you must be securely logged in with your work or school account or your Microsoft account before using Cortana, and some consumer skills including music, connected home and third-party skills will no longer be available in the updated Cortana experience in Windows 10."
Users still will be able to do things like control certain smart home devices and speakers -- including the Harman Kardon Invoke -- via Cortana but only using the Cortana apps for iOS and Android, a Microsoft spokesperson confirmed when I asked. Oddly, users will not be able to do this using the new standalone Cortana app on Windows 10. If you have an Invoke speaker, which is powered by Cortana, and you want to keep using it, you'll need Cortana for iOS or Android. Windows won't be an option for controlling it at all, the spokesperson confirmed.
Microsoft is going to require users to be signed in with work or school Microsoft accounts in order to use Cortana in the name of security. The more advanced productivity features of Cortana will be available only to U.S.-based users to start; those outside the U.S. only will be able to get answers from Bing and to "chat" with Cortana until some unspecified point in the future when Micorsoft is hoping to add more Cortana capabilities for international users.
Update: For those wondering, the ongoing work between Amazon and Microsoft to integrate Alexa and Cortana, with Alexa handling more of the mundane consumer-focused queries often asked of digital assistants, is still happening.