TL;DR: start a business that sells a (possibly premium) hosted version of the project, sells training/support for the project or try to extract sponsoring from your users.

It's less a "pay your rent with your open source project" article (as the title suggests) than a "start a business that happens to produce open source software" article. Also anyone with one or two smallish libraries need not apply, this is about projects with person-years of effort invested in them.