If there are no specific examples that would use the functionality then that means we don't need it. I wouldn't generalize for the sake of generalization. See my latest email on the pydy list. My biggest suggestion here is to create examples problems you want to be able to solve (we've already created a bunch for multibody dynamics) and then design API around the practical things you want to be able to do. This is then much easier for outsiders (i.e. outside the details of your code) to understand and digest.