I developed two titles with the Unreal Engine and whilst initially UnrealScript seems like an advantage it very very quickly becomes problematic. My favorite being the dependency of the C++ code on the script and the script on the C++, so if you're not careful you can end up being completely unable to do a build.
As much effort as they put into the IDE it would always play second fiddle to Visual Studio. When I left there was no way to remote debug unreal script on the target device (this may not be the case now).
I know that all of the guys I worked with in the studio would welcome pure C++ approach. The only real losers here are mod makers who will have a higher entrance bar.
The modmakers don't suffer too dearly, blueprint can do almost anything a modmaker could want, and in the future perhaps we can drop the almost.
They didn't really drop the highlevel language, they just dropped the idea of a highlevel general purpose language, favouring a strict DSL.
There's still a bit of interop, but you have to be very explicit about it. In C++ you use macro's to tell the compiler what's accessible to blueprint, and to access blueprint from C++ you have to make weird queries that are very obviously highly dynamic and ill-performant.
We ended up prototyping most things in UC then converting most of it to native code for performance reasons.
The reason builds were sometimes a bit tricky was due to chicken and egg syndrome because the script compilation wouldn't just compile scripts, but also modify headers to support the new objects created in script.
Aside from the performance issues, the main drawback (to me) with UC was definitely how tightly coupled to native code it was.
They could also use C# instead of UnrealScript on top of C++. This way you would be able to leverage the Visual Studio while getting one of the best languages. It would make Unity3d guys welcome once they need something better as well.
To second what scott_s said, you'd have a huge interop layer. The fact that C# has a closer match to C++ types and primitives doesn't mean you have no interop. Unity has a huge surface area between the C++ parts of the engine and the C# parts of the engine; a ton of work goes into maintaining that, and it complicates porting to new target platforms like the web (can't just feed everything through emscripten).
Yes, C# and other .NET languages are nice, but the open source implementation (Mono) ends up being difficult to port to novel platforms due to a combination of technical and legal issues.
As much effort as they put into the IDE it would always play second fiddle to Visual Studio. When I left there was no way to remote debug unreal script on the target device (this may not be the case now).
I know that all of the guys I worked with in the studio would welcome pure C++ approach. The only real losers here are mod makers who will have a higher entrance bar.