Looks nice. Would there be a native version, for which data are only stored locally? You would certainly have some professional market with that. I would pay for it just to replace LaTeXiT.
I recently released Vexlio (https://vexlio.com), a desktop (i.e. non-browser) diagramming application, that supports editing of embedded LaTeX equations which you can then easily export to PDF, SVG or PNG. Currently Windows only, but Mac is coming very soon now.
Interesting. If not confidential, what language did you use to create Vexlio? and what library (if any) for PDF and PNG output? Asking since PDF generation is one of my interests.
Not confidential -- Vexlio's written in C#, and uses Xamarin.Mac for the bindings to the Mac world. PDF and PNG are both generated by the Skia library (skia.org).