I had worked on some basic framework for electrostatics during my first GSoC. Then we realised that we needed stronger vector functionality, so I diverted my focus to developing physics.vector, and then sympy.vector.
You can see my pull request here -
https://github.com/sympy/sympy/pull/2361You could maybe make a wiki page and share your thoughts and structure so I could help you develop it further?
For vector maths to supplement your code, have a look at the code in sympy.vector package. I never got to getting in the docs, which I will get to soon. But you can see the pull request for it here-
https://github.com/sympy/sympy/pull/7860The code is pretty much merged. So feel free to try your hand at it, and suggest any new functionality that your ideas may require.
Cheers!