When it will become the Windows 10 default is an interesting open question right now, and the exact roadmap doesn't seem entirely transparent yet. This move to the Beta release channel seems to indicate possible confidence in it.
Windows 10 isn't the only target market though. Microsoft has made it clear they want Windows 7 users, the odd minority of users still on Windows 8 and Windows 8.1, and even macOS users for this new Edge. This "cross-platform vision" was supposedly a key reason to rebuild on top of Chromium in the first place.
(Interesting rumors even state that Microsoft is hoping to push it as the "final" default browser for Windows 7 in a final security/feature update/mini-service-pack roll up sometime before the April 2020 end of security date for Windows 7 in a hope of leaving Windows 7 at the end of its ordinary security support life and the start of its extended support phase in a better place than Windows XP was left.)
This will eventually replace the current Edge on Windows 10, so the answer is "yes - sometime in the future". Additionally, it's already available on Windows 7 and 8.
To me, this means many developers will be more able to argue the case for deprecating IE11 support.