Hi,
SpeedTree has been acquired by Unity (https://store.speedtree.com/unityannouncement/) and this could make a crucial technology for open world games possibly an exclusive tool for another game engine.
Is Epic planning a replacement for it?
Otherwise (thinking in the long run), what other reliable tools could be used as replacement of SourceTree, with comparable performance, quality and creative freedom?
obviously, UnrealTree, 
unreal step by step is cleaned of relying on third parties, so an UnrealTree will not be rare to see.
i heard megascans was working on something.
I haven’t seen anything about exclusivity. Probably, just like tools acquired by Epic, SpeedTree will still be available for other engines, i.e. Unreal. Unity has done the same with Plastic SCM too: Sure, integration to Unity might have improved more than UE4’s, but it’s still available to UE devs as it always has been.
It wouldn’t make much sense to lock it to Unity imo, since they would lose subscriptions. Most likely Unity will have better / seamless integration.
Epic and open world are 2 things that don’t really go together in the same sentence, unless it’s a sentence about how they do not go together like this one …
There is no mention of exclusivity. Like the tools acquired by Epic, SpeedTree will probably be compatible with other engines, like Unity. While Unity’s integration with Plastic SCM has improved over UE4’s, it’s still available to UE devs as it always has been.