"Deep Dives" can be farmed out to contractors and you dont have to worry about paying employees.
On the fully indie side of things Michael Hartl has been doing it for a while with Ruby, front-end technologies, and seems to be doing OK for himself. I don't know what kind of profit we're talking about but it seems that it's enough to keep at it. https://www.learnenough.com/
Then there's Udemy. Max S. has 1.4 million "students" which I believe means his courses have been purchased a combined 1.4 million times. If we assume an average selling price of about $10 that's a lot of money even when we subtract Udemy's cut of the money. https://www.udemy.com/user/maximilian-schwarzmuller/
In general, be thoughtful when considering what you think "makes money" on the web. While not easy to achieve, there are a lot of folks making very good livings selling things on the web. But of course it's not going to make headlines if they are "only" making $100K or $500K. The press is only really interested in gaudy public stock offerings worth billions.
In the specific case of MDN, it certainly seems like they could sustain themselves using this model. If 10,000 people sign up and pay $10 a month that's $1.2 million/year in revenue. Certainly enough to pay for a rack of servers, some dedicated staff, and a rotating cast of outside contributors to write the articles.
It is absolutely possible to make money selling classes/tutorials (e.g. via Udemy or any of a variety of other online class platform), but MDN is already committed to making its classes/tutorials available for free https://developer.mozilla.org/en-US/docs/Web/Tutorials
It's an essential component of MDN Plus that they have to say exactly what they say in TFA: "Nothing is changing with the existing MDN Web Docs content — this content will continue to be free and available to everyone."
As a result, MDN can't practically sell books OR classes. What's left? VIP access.
Yeah, sure, slightly different models. But plenty of people are selling this kind of content and achieving financial success -- and that's without the benefit of MDN's brand recognition. Clearly, it can be done.
What is your point now? That these counterexamples don't have the exact same % mix of free vs. VIP content as MDN is proposing, therefore MDN can't financially sustain itself? Seems like quite a supposition. I see a wide variety of free/VIP % mixes out there. Doesn't seem like there's one right answer or magic formula.
MDN may or may not succeed with this model. As with most things it comes down to execution. It's relatively new territory for Mozilla so I'm not convinced they'll pull it off. But it's not like some wild and untested/disproven model.
Sure. They're often called "ebooks".
However, back to the topic of corporate sponsors.. I see a distinct lack of calling out who the sponsors are? We all know a lot of VERY big companies shut down their own doc efforts to throw in with MDN; why not sell them call-out spots on a list of sponsors? Tiered even? Doesn't have to be super intrusive but would potentially open up funding channels within those large companies.
It can be done on a small scale. The name escapes me but somebody big in the React world recently put out a course and made well over 5-6 figures in the first day of preorders alone.
Now whether that scales to fund an entire organization or corporation remains to be seen.
Charge for the "Pools, Hot Tubs, and Beaches" content?
I would always trust open, free deep dives under open scrutiny and criticism more than something behind a paywall.
Even if this is from Mozilla.
A premium chat room/forum would have been miles better.
Yes, they got rid of most of the team, bu the remaining team members that are there and pretty much all of the community contributors would quit if they were suddenly transitioned into paid tech support roles.
We know how to do this "correctly." MDN Plus should be a VIP pass to access to the MDN team, via a private forum and/or chat room. Talk to (survey) the paying users for what new material they're interested in, and provide that.
This is how basically all Patreons work. People buy those subscriptions like hotcakes, they have excellent margins, and the subscribers are reliably very satisfied with the result.