UVMap issues, and ideas..

[micheus]

I'm going to need to "stitch" 300, 400, ... or even 900 or more Tetrahedrons. So I'll need to see what parts of stitch can be available to a plugin.

Usually we need to unwrap the mesh with care. Is impossible to guess how the user wants to unwrap the model - we can just try some options.
In your case, with so regular shapes, I know you probably would be able to automatize the process.
The use of Stitch was necessary just because all those edges were set to hard edges and - as I told - the hard edges in the model are automatically used as edges for cut. If you don't want use them for cut, then you need to unmark them.