It's more or less the same underlying approach as Hamachi: L2 virtualization. The execution is a bit different, and it's designed to be more sysadmin-friendly to enable its use as something like a cloud backplane network.
As far as the future goes, I have different and I think broader goals. VPN is just the first application. I have others in mind.
Right now it's charging for the convenience of setup and administration on zerotier.com. You can run your own "netconf master" and create your own networks, but it requires some system administration and Redis database wrangling.
Generally the people who will pay you are the people who want convenience, like business users, and the rest are people who won't ever pay you anyway.
The supernodes are not part of the business model. That architecture just exists to make the system fast and secure by providing managed anchor points. All traffic is end-to-end encrypted so the supernodes can't see traffic content.
