I never asked a question here just based off curiosity, but here goes. Im not a programmer, but I am familiar with basic programming and always hear that C/C++ is much more efficient than higher languages like Java and Python. Would there be any difference in speed if Rhino was based off C++?
Rhino (in its core) is based on C++, and you can make plugins with C++.
There’s also a .NET API (RhinoCommon) so you can use C# and VB.NET, and IronPython.
// Rolf
Answer solely based on your title: 
What if Rhino used C++ instead of Python?
Focusing on the word instead, not being along with.
Result will be a global-wide civil movement protesting inside tents in front of every McNeel office.
More radical individuals will be DLL injecting in order to get Python2.7/Python3.6 working on Rhino releasing free tools that do it at system boot 
Now on the topic, I’m not so much of a programmer but unless you build a software optimized for specific architecture, and you don’t mind re-writing for other architectures.
Or unless you wanna waste time optimizing the app for the non-optimized Windows (I have never used Mac so I’ve no idea there), everyone is better off with Python and/or csharp.
On the other hand, what do I know, let’s use ASM. We can make Rhino run on an electronic calculator or better a gameboy