I like your initiative to abstract USB keyboard functionality (and others) into a C++ library/class. It's also great to read some of your Python examples (even though I don't know it).
I just tried to write a core with V-USB, and it seemed like there would be no good way to make each project independently configurable. This is mainly because of Arduino's build steps, which do not allow any part of the core to depend on a part of a sketch.
V-USB and Arduino's IDE just don't mix well.