Cyberpunk 2077

If you're specifically working on a game that stock UE5 can't do, e.g. you need to make the kind of far-reaching changes that Valve had to make to Source to make Portal possible, you end up with most of those problems even if you're doing it by modifying UE5 rather than modifying your in-house engine. You're still ending up with a custom engine at the end of the process and still need to make tooling for it and onboard everyone, even if it ends up fairly similar to stock UE5 due to being modified UE5. It doesn't necessarily work out any more scalable or sustainable than modifying an in-house engine once you're making this kind of change. The outcome ends up being that games that can't be made in close-to-stock UE5 just don't end up getting made.