Don't forget text plotting, that's the hard part. The technical challenge is not huge, but the amount of small and "easy" features a good plotting lib needs is huge.

It’s easy if you keep it simple, your data is regular, and you don’t handle the multitude of corner cases. Doing it properly is about as difficult as processing Unicode correctly, which is to say quite bloody hard.

Lol if you have tons of free time on your hands. I'd like to see your replacement for gnuplot that has all the same capabilities. HackerNews will be awaiting your contribution!