> The reason I use plain text is that nobody has made a similarly universal format for multimedia
Care to explain what you mean with multimedia? What is missing with the existing audio/video/picture-formats?
> And because of that, ordinary people (and tech geeks) don't have a way to personally utilize and store their copious multimedia
There are dozens of tools to organize and utilize your media-content? Kodi is widely used as I know.
> For example, there's no good way to backup your Snapchat or Facebook page,
How is this the fault of the FOSS-world? They can't dicate a company what they offer and what not.
> or even better, to create an equivalent locally.
Yes, but for what? What is Facebook or Snapchat in your mind that it would be even neccessary to create it locally? But, there are tools with similar function. It's just not simple to use, because such services are not simple by they their own nature and nobody, neither FOSS nor commercial world, has made it simple enough yet to setup services for any random user.