That is quite fine. I have a few examples from "The Mathematical Mechanic" that I am sure you'd love. Yours is quite in the spirit of those examples, especially the last one.

http://www.cut-the-knot.org/pythagoras/MechanicalProofs.shtml

The area sweeping comes up in a little different setting:

http://www.cut-the-knot.org/Curriculum/Geometry/PythFromRing.shtml

I think I'll add your musing as a comment to that page.