Well R and Pandas cover data analysis for the most part, while is is a computer algebra system? Seems like apples to oranges, really more comparable to sage/mathematica.
Uhm... it says right at the top of the linked website that sympy is used as the backend.
Remember I'm not qualifying the value of this project as a replacement to Mathematica. I'm asking who is the segment bthat would use this as opposed to going directly to symPy or R.