Epic Games updated UE4 roadmap pages, in the Future Releases section:
I would be surprised if that is going to happen anything later than 4.26 It seems pretty obvious that they need it for their own products and quickly adding support for Mobile too clearly hints at Fortnite as other developers suggested in this thread. Which is a good thing for all UE4 developers anyway. The APIs should quickly become rock-solid with bugs fixed at least that seems obvious. And I’d say along with Niagara and Virtual Texturing. These APIs got a development speed-up clearly for a reason.