Would you mind to argue and elaborate more the reasons why a new space sim like a theoretical "Elite Dangerous 2" would not take advantage of being developed on an existing engine like Unreal or anyone else, rather than on an unfinished and propertary engine (that no other developer knows outside their company).
Which are the pros and cons for this choice? Is there any "real" expert here that could explain?
Part of such a decision is about competitive advantage in a cut throat business environment.
Shifting to xyz engine is very likely similar to starting from scratch, hence you have to consider the cost of parallel developments, enormous cost and risk - orphaned software development for example - before return on investment, and such move will cause additional stress, unpleasant HR turmoils, turnarounds in the 30%-40% region are standard!
Licensing another engine also means you create dependencies that you avoided with proprietary solutions. If stuff doesn't work as it is supposed to, you can handle it in-house, if you are a license holder your company relies heaviliy on external service .... well, I can tell you, I know how THAT feels if stuff goes wrong over a prolonged period.
Proprietary lacks the option of external code reviews, on the other hand, there are no compliance issues to worry about.
Biggest draw back of proprietary I can pull out of my head, some fixes may never happen, hence using constant workarounds, which in the worst case can cause "bloatware" and more.
All in all, currently I think, this is a very easy business decision for FD: Cobra it is!
P.S.
Can someone please hack the global dictionaries and scratch the term "Expert", please? It is as useful as a tick under your armpit.