Hi Bohdan,
Our physics engine is Chaos moving forward, over time some of the abstraction code will be removed as we do work in that area. Box2D isn’t supported internally, but is very mature so likely to be available for a long time (although I’d check with the creator if you need certainty).
Of course with us being open source, other creators can provide alternatives if they like, but they won’t be supported in house.
Best
Geoff Stacey
Epic Games