The project is called Scikit-HEP. Notice the upper-case "S" and "HEP". That is distinct from the package scikit-hep.
Like "sy-kit happ"(y), forgetting about the "y" in "happy". Of course "sci" stands for science.
You are most welcome and encouraged to get in touch via the resources listed at Getting in touch. Please also refer to each package repository and browse through the list of "issues" or files CONTRIBUTING for details on how to get involved.
It's a nice idea. Support for PyPy across the various packages could be envisaged in the near future but only once the scientific stack based on NumPy supports it. This being said, certain packages do support PyPy already.
Support for GPU-oriented code is not foreseen as default but some of the packages envisage it in the near- or medium-term future. Please refer to the documentation of the various packages.