I'd like to be able to continue a spline after it's ended. This option would allow the spline to "continue" from the start or end point of the selected spline as if it were originally drawing that way.

The work around right now is to trace over the existing Spline and then continue. Or create a 2nd Spline and make either tangent/CC and then use a Fit Spline over it so that there isn't a break in the surface where the two Splines meet. And this is assuming that the original spline has not had any of the handles adjusted.

Or offer "Fit Surface" but that'd be a whole other ball game right there.

Additional control for Splines in regards to the Control Polygons as they are used in a sketch. Being able to add/subtract without changing the Spline in anyway would be a nice addition as well.