I've been focusing only on timeless content (for as realistic of a definition of "timeless" as technology allows) for Practicing Ruby, because I think it's more compelling and sustainable as a work for the benefits of the commons.
In other words, if I can look at my archives as being a body of materials that mostly holds their value over time, then supporters can be comfortable knowing that their money is stretching far and wide.
Also, although we don't do it as often as I wish we could, I like the idea of periodically going back and revising or replacing old works with updated content, to extend their life even longing and take advantage of new thoughts that come along. Having paid supporters really helps there, because it feels less like a chore and more like a service.
As for perishable / time sensitive content... I don't really know. I guess in that case you're funding people for their time and expertise rather than the lasting value of the work they do. I think this would come with a very different set of challenges, but I'm not seeing where the economic problem would be.
In the first couple years of Practicing Ruby's development, we did release the content only after it had been available to paying subscribers for a while. (There would be 10-20 articles available to subscribers only at any point, with a sharing mechanism that allowed folks to post links for others to jump the paywall)
When we stopped that and moved to directly releasing content when it was ready to be published, there was no major change in subscribers immediately, or even within a six month window after that decision was made. Actually, the cancellation rate went way down, so that might be a sign that the supporters were supportive of the idea.
The problem (and I'm sure some folks here may have guessed it), is that once everything was made available for free right away, the number of new subscriptions went way down. Whereas before we might see 30 new subscriptions a month and lose 20 people, we started seeing 1 new subscription a month and lose 2 people.
A sequence of events that happened since then has slowly bled the business of its revenue, although our traffic improves every week, even without new content being published for several months at a time. The most notable one is that I decided that the business ought to run on its own revenue, something that is ultimately a good thing but was a harsh change because previously I'd work 120+ hours a month on the project and only just barely squeak by on a subsistence level.
So basically, the project went dormant for the better part of a year, and although I did some small things from time to time, I mostly saved up the revenue so that I could pour more dedicated time into things down the line. In that process, we understandably lost supporters over time, but the main issue was bringing in new subscribers.
At this point, I'm burning the modest reserves I stored up, and that's given me a few months of runway before the project needs to go dormant again. If the collaborator model works and the kickstarter I set up gets funded, I think I'll be able to stretch things a lot farther. I do a very intensive process with anyone who contributes their work, but at this point it's still much easier for me to collaborate with someone who's contributing ONE article to Practicing Ruby than it is for me to research and write ten more pages when I've already produced something like 1000 pages of work.
So in a way, the death knell rang, and that's what motivated me to try to fix the business problems. In the process of doing that, I remembered the motivation for doing the project in the first place (which was to provide a functional example of a top-notch free documentation project), and that's what got me excited about things again.
Who knows what will happen from here? Maybe the project will still die. But either way, I'm sure I'll learn a lot from it.