It's no secret that Cortana is losing favor with the PC-using public, and possibly also with Microsoft developers in some departments. A well-regarded Windows-focused leaker claims to have found evidence that the digital assistant may be replaceable in future versions of the OS. This is also somewhat corroborated by the fact Amazon's Alexa is now available in Windows' Store.
https://www.notebookcheck.net/Windows-10-may-allow-you-to-pick-your-own-digital-assistant-in-the-future.382211.0.html