[jjs]

As it happens, I'm working on something like this right now...

My current best solution is to use mouse/pen movement as cspline sample points, even when not drawing. The motion as you swing into a curve, even before the pen touches down, often predicts the trajectory of the pen stroke. (This also lets you "swing in" a circle without getting ugly linear segments).

This may be of limited utility on a touch-based device, however.