Just to throw my own experience in.
When i started 2 years ago with UE4 i saw Blueprints and immediately hated them. I didnt want to use them and hated Epic to force me to use them (partially, AnimBlueprints ftw).
Then i though about publishing something to the upcoming marketplace, and i already had a topdown system for my own game. And, omg, no code allowed at that time, Blueprint assets only.
Well sh**, ok, i need to convert everything from C++ to Blueprints.
Fast-forward 3 months:
I fu**ing love Blueprints! Iteration is so fast (with the obvious flaws when you could do something in code with a short line and need 5 nodes in BP to do it), if i need anything exposed to Blueprints that wasnt yet, i just expose it myself, if i need helper functions (array sorting and general array handling as a prominent example) i just code that and expose it via Blueprint macros. Setting up replication is a breeze in Blueprints, as compared to the code version (and even with unrealscript i had a hell of a time with replication, making everything work correctly).
Also i often hear so many people ranting about performance, and how blueprints are so slow compared to “fill-in-anything-you-want-”. Most of these people never had any performance issue with Blueprints and dont have any idea how the VM for the managed code works. They often think “well, my function takes n milliseconds in C++ so it will take n*10 milliseconds in blueprints. bad performance everywhere!”, when its actually just the call out from the VM to native code that has a performance issue and takes time.
Agreed, a few people do have performance issues when using Blueprints. And from my experience its 99% not the fault of the Blueprints itself, but really bad coding. This is actually the real bad thing with BPs, you are tempted to ignore programming patterns or think you dont need to know what you are doing. When i see people filling up their Tick events with code and then blame Blueprints to be so slow, i really want to slam my head on my desk.
So, talking about C#, its fun. Its also slow compared to C++, since its also managed code (the people demanding C# as a scripting language wouldnt use any @Unmanaged annotations in C#). Iteration times would probably a bit faster than with BP since you dont have to draw lines. But the intellisense will never be as forgiving in searching as the blueprint search. Also i have yet to see how intellisense performs for C# on an API that would be that big.
Just my 3 cents.
Cheers,