But then why hasn't open source stepped into the breach?
This seems like the kind of thing that a single, dedicated hacker could crack wide open.
The pieces are all commodity, no? People can buy lenses independently, so you don't have to design those. Everything else should be COTS--processor, networking/cellular, display, etc.
It might not be super cheap, but it shouldn't exceed $500 on the BOM. And then people can iterate on it over time.