HI DesuDeus, yup I've looked into Spiro before, it's pretty cool!

One of the difficulties with it though is that it's not just "mostly for" 2D work, the whole mechanism actually only works for 2D planar curves, it's not something that can work on a curve that needs to bend around in 3D space. So that means it could not work just as a fully general replacement for curve interpolation, it would probably need to be a special mode or something like that.

Then the other problem is that the library itself seems to be abandoned by the author, I've contacted him about licensing it but he seems to be too busy with his new work at Google to be able to focus any attention on anything to do with the Spiro library.

And unfortunately the library that he has released is under a license that prohibits its use in commercial applications like MoI, the library is allowed to be used in Open Source applications only (like Inkscape for example).

So currently it does not look like it is possible to use it inside of MoI.

In the future I want to experiment with some kinds of energy-minimization for curvature distribution which may give a similar effect. The most interesting thing about Spiro curves to me is not just continuity but more about the nice and even distribution of curvature along the curve.

- Michael