Chrome extensions are just another interface to a web app. They're easy to reproduce by another hacker, but most people won't bother reverse-engineering an extension just to get it for free. You'll probably sell product to people who don't know how to do that, anyway.

If you're concerned about it, then just make sure the IP doesn't live entirely in the extension itself with a simple third-party authentication & payment system.

There are more than a few companies set up like this already. SalesLoft started as a paid Chrome extension!