"Setting up a company can help because it will let other researchers support the project by buying the software on research grants." This is absolutely correct, and has happened many times now in the last few months (I started the company itself a year ago).

By the way, another way to get financial support for an open source project is to sell a short tutorial book. For example, the creator of Laravel did this on Leanpub (disclosure: I'm a co-founder of Leanpub) and did pretty well: https://leanpub.com/laravel is #7 in lifetime earnings on Leanpub. (Also, one of the core contributors on Laravel has done even better: https://leanpub.com/codebright is #2 in lifetime earnings on Leanpub.) Similarly, the creator of Trailblazer is doing pretty well recently with his Leanpub book: https://leanpub.com/trailblazer is #9 in revenue over the past week.

Anyway, my point is that even if you're in a niche, if you are the clear expert in that niche (say if you created the framework, or in your case, the software), then a book may be one worthwhile component of a monetization strategy. If you can sell a $30 book to 4000 people, you can earn some decent money. (The royalties on a $30 book on Leanpub are $26.50, so multiplying by 4000 results in over $100K.)

“Given that writing good English is a rare skill among programmers, we can ill afford to lose manuals this way.”

https://www.gnu.org/philosophy/free-doc.en.html

Even more if you can tie it in with enough topics for a textbook.

Hopefully one day textbook prices can return to a sane level, say between $30 and $80. Today's textbook racket (I don't want to call it a market) is obscene.