This is pretty cool! I would love to see this kind of tool (including the LaTeX output) available for other kinds of diagrams. Sequence diagrams, box-and-line diagrams, etc.
Diagrams for homework is easy. The tool almost doesn't matter.
What gets hard is when a diagram is describing something you don't have control over, such as a system built by dozens of engineers, or a product that is still being influenced by changing requirements. In those cases, I often want to build an initial diagram, then extend it quickly and in a version-control friendly way, or even in a way that can be generated.
Extending a Tikz diagram (by additional lines/nodes, I assume?) just means adding more Tikz commands to draw the additional parts. If you mostly use automatic or relative placement, the diff will be fairly compact. If you use manual placement, you'll get some noise from the adjustments required to make space.
Caveat: I have only used Tikz for homework. However, I didn't usually have control, and the diagrams occasionally had to change when I realized I forgot some part.
