Rather sad the two proposals here are either "giant browser vendors should pay for it" or "independent web developers should pay for it." It's one thing for developers to pay for things that will develop their independent careers, but MDN is a reference as much as it is a learning resource; it's something developers constantly use at their jobs. Their employers, big or small, should be the ones paying for it.
Of course, we all know that asking startups to actually fund open source (whether code, documentation, or learning resources) is like pulling teeth. I'd say maybe the collapse of some larger open source project(s) could convince companies to start actually giving a shit about whether or not the maintainers of the technology their entire businesses rely on have enough money to continue developing said technology, but it's more likely the companies would just say "well, let's put 10 engineers on this problem for a month to replace this dead open source technology with something new and shiny" and not recognize how much more they've had to spend. Or, y'know, they'll go with paid support of a Microsoft product or something.
Of course, we all know that asking startups to actually fund open source (whether code, documentation, or learning resources) is like pulling teeth. I'd say maybe the collapse of some larger open source project(s) could convince companies to start actually giving a shit about whether or not the maintainers of the technology their entire businesses rely on have enough money to continue developing said technology, but it's more likely the companies would just say "well, let's put 10 engineers on this problem for a month to replace this dead open source technology with something new and shiny" and not recognize how much more they've had to spend. Or, y'know, they'll go with paid support of a Microsoft product or something.