Hi Rob, for 2 splines you can currently make a surface between them by using Loft.

For a single non-planar spline, that is going to need a special "N-sided patch" tool which MoI does not currently have. I do want to add that in to MoI, but it tends to be a finicky tool so I'm not exactly sure when that will happen, but not for v2 so I guess not "in the near future".

- Michael