Oooh, you won me over with the placing text and labels part. That's great!
That said, I would not pay for this. Python has an awesome free and open source ecosystem, I cant imagine using pytorch, scikit learn, numpy, pandas etc for free then paying to annotate my plots.
- educational features such as tooltips and explanations for common python and matplotlib functions;
- commercial use;
- educational use (as part of a curriculum).
- potentially, export to other languages (Julia).