That looks pretty good.

Studio's rigging tools had (has ?) the "Figure Mixer" which did exactly that: Mix the rigging of two figures with identical mesh.

I did some Mike 3/Matt  and Hiro/Luke hybrids, but in the end I stayed with hand-editing meshes as children normally don't grow in a strictly linerar way so I had to re-rig them anyway. Clothing was a problem, too.

But this looks like a good way to "purge" some of the "stylized" out of V4 and M4 and to generally add some variety into a character's built.

Seems you solved the clothing problem, too.  Congrats !

Never was able to figure that out with Studio's "Figure Mixer".

I wonder if it's possible to "freeze" the rigging of such a combined mesh to use it for standalone figures.

I.e you can sculpt your figure any size and proportions you like and then scale a donor figure to match that figure and then freeze its rig and use it for your new figure.

Instead of having to match your new figure to an already existing rig unless you want to rig it completely from scratch.

Anyway, good work as usual. For $5, this should sell pretty well.

:-)