Monetizing plugins will inevitably end in disappointment. Why? Because when you monetize something, peoples' expectations change. They expect it to work perfectly, they expect to be able to extend the code, endless support, and we know that the world of development is a little more complicated than that.

Also, there's never been a better time to enhance your development via crowdsourcing. It's arguably more productive to allow feedback and open-sourcing of plugins than to confine it to a private team.

The perception that the only reward for producing a plugin is to make money, is fundamentally flawed. If your plugin is popular enough, there are various ways to leverage this popularity and turn it into potential business.