Thanks. Interpolating between map projections that have the same clip region is relatively straightforward. When projecting geometries from the surface of a sphere to a 2D plane, you're always going to have a discontinuity somewhere on the sphere, i.e. the clip region. The projections supported so far all have the same discontinuity along the antimeridian (the meridian at longitude ±180°).

Extending the interpolation to work for projections with different clip regions should be feasible but there are several ways to interpolate between arbitrary shapes in 2D, so I'd have to give it some thought.

Another way to transition between "polyhedral" projections like the Dymaxion map and the Waterman butterfly is to fold and unfold the maps in 3D to and from a closed polyhedral globe.