I like it, overall. Definitately would be interesting.
My concerns:
1 - Places like where the lightbulb was invented are interesting and historic. But many inventions are invented by R&D departments at corporate laboratories, not so interesting. Would this category include those inventions that come from the corporate labs of DuPont, for instance?
2 - I'm not certain about this, but I believe Thomas Edison made most of his inventions at a single location. Would there be a waymark for each invention that shared the same coordinates as they were both invented at the same location?
Just some of the thoughts I have going around in my head. Like I said, I like the idea and I'm curious to see where you go with this.