Yeah, but having that is clearly not aligned with making money. They could make it more difficult or impossible to use headscale at any moment.
Once a FOSS ecosystem exists, it can always be maintained as such.
What may theoretically happen is that the same client won't be able to join both an open-source controller and a controller from Tailscale-turned-evil.
I suppose that corporations, especially those without huge IT departments, will and do happily pay Tailscale the reasonable money, and have their secure VPN just working. For them, it's no different than paying for Zoom or Office365, only cheaper. They totally do not want to depend on in-house networking expertise.
So I think Tailscale will be doing well financially,
The thing is, what makes tailscale works really well as a "central" control server is that it makes a lot easier to connect your personal machines. You don't need to deploy your own server, or mess with networking stuff. You just download it, log-in and there you go. I myself have invited some non-tech friends to my network for playing lan games from time time and they find pretty easy to setup tailscale on their side.
[1]: https://github.com/juanfont/headscale