"Less than 100% reliability is essential for the sustainability of an off-the-grid solar system."
IMO, this can only become mainstream once there is no longer an expectation of "100%" uptime for websites in general.
It's far-fetched, but I can imagine it becoming mainstream if mesh networking becomes popular, or if the Internet were to become a widely self-hosted platform (e.g. people had their own "clouds" running in their homes). In such situations, 100% uptime would no longer be an expectation, so the perceived cost of using an off-the-grid system would be reduced.