There's a way to install Mypaint on the N9.

Search the forum for easy debian and how to install it on the N9. When done you should be able to install Mypaint through synaptic app manager (think it's called that) and you should be able to open it from inside easy debian (lxde). You'll have to live without pressure sensitivity as that is gone with the capacitive touchscreen on the N9, but hey people are making some pretty awesome artwork on ipads and such, it just takes a little more time to get where you want without pressure sensitivity.
You'll also have to live with either fingerpainting or/and with a capacitive stylus. Neither is totally accurate, but then you just need to do some more zooming.

Happy doodling on your N9 if you get there

Dousan...