I hate to compare MS Paint to paint.net but..
MS Paint has custom brushes built-in like watercolor brushes/crayon
As of now, paint.net only has paintbrush and pencil. Thats it.
I'm not asking for a plugin though, im asking why not implement this into the main program?
Also, why not a custom colors, paint.net has this, but it doesn't make it so you can make the color, then put it into the pallete without changing the actual text file. If you don't know what im talking about, check this video