There is not really change, extending of engine code (which C++ programming in UE4 is) was always there, but not accessible from free licences (like UDK). Also Blueprints are not C++ modules (and they not really C++ modules as they all being compiled own to machine code), it’s using same virtual machine that UnrealScript used, which are bindded to native APIs as most other scripting solutions, so perfermence is no diffrent from UnrealScript.
That might workflow reason as you say, blueprints are simply more accessible… and i think Epic didn’t expected so much C++ allergy in community 