Legacy PhysX will probably be kept in UE4 for some versions otherwise anything using it should be quickly updated to Chaos… Also if Chaos is for destructibles only in its initial version then it is going to take probably 1 if not 2 years to see PhysX completely replaced for everything (let’s speculate that maybe by UE 4.29 or 4.30 Chaos will be fully complete and PhysX gets removed)