I totally think this would be a good container format for these various interactive tools. I think one of the reasons why they are not daily tools for many classes is that so much of math is symbolic. So far symbolic math has been confined to paper, even if a district decides to pay $100 per student per year for access to one of the existing services that will nicely collect your students final answers and machine grade them, students still do their work on paper, and the software is oblivious to it.
On tools like Geogebra, I think we need more interactive tools, but they need to exist alongside the symbolic work that everyone needs to do in most of their classes. Managing a classroom full of students working on computers (which can be distracting), is hard to justify if it is only displaying supplemental material and you also need to transition to "normal homework time".
I definitely need to add a generic diagram editor to make this useful for classes like physics.