If I'm independent, I always work fixed fee & payment schedule. When I've had a big company at my back, I've also worked at X% of realized revenue, capped at $Y.
Now, the important thing this implies is ownership of the outcome. I'm not building "a website;" I'm building "an e-commerce product" (or whatever) with all the expectations that come with it.
Back to the article... looking at the rates again, I think this is the author's next step in pricing. They're obviously very good. To make it as an independent developer, you need to have a clear understanding of value anyway - so why not just estimate the outcome ahead of time and benchmark against it?
Though it is still just potential value. There has to be some sort of payment for the early stages if you’re not planning on taking the same risks along with your client.
I have never worked on building any project like that so I’ve no idea but I guess the maintenance and future work could be tied to a percentage of the revenue generated for the company.