We're still very early in the life of UE 5 and UE 6 won't be there for a long while. There is still a lot of improvement to come to UE 5. For example, they will apparently finally put much better multithreading in 5.5.
I personally hope to see nanite in Combat Pilot, which seems to be very well suited to a flight sim where you go from being very far to objects to being very close up, so having an optimal level of detail at each level would allow for great visuals, without pop in.