It doesn't seem impossible in principle, but anything viable has to be better than any open source tools that might be out there but also able to command an audience with enough money and inclination to pay for it despite whatever level of license infringement takes place. It sounds like quite a narrow scope!
(yes the domain name is silly, rebranding is on the todo list but customers come first).
It has plenty of customers paying a $45/month subscription, some of which are big name companies that unfortunately don't like to have their logo put on the web page. But it's a CLI tool, and it's monetized. What do you want to know?
In my space, some larger competitors are more focused on SaaS/cloud offerings. But that can be a mixed bag for security-sensitive customers who prefer to self-host, as well as for folks who want to integrate a tool into an automation/CI/CD pipeline. CLI tools are more compelling in those situations.
Fun part is that the CLI handles all the browser redirecting for the payment and saving the license (I guess). Just pass it a `--pro` arg and there you go.
But I’ve seen REPL instances (which are command line in a way but interactive) monetized. The AMPL optimization language is monetized. The very expensive KDb+ language and database is monetized.
Back in the day lots of DOS shareware tools like pkzip, etc were monetized as shareware.
Bought it to transfer mail from SMTP to Office365. Worth every penny.