This is actually horrible for society as it implies that the Web Browser will have to implement a billion different parsers for all of the separate file formats it supports, which not only causes it to have a ridiculously large attack surface but pretty much implies there will only be a couple serious separate implementations (if even that soon...) as it is just too difficult for even a large company now to build a browser.
Meanwhile, it doesn't even ensure the property of being able to view source, as people can and do obfuscate things they don't want you to see, and if people want you to see the source code there is nothing preventing them from making that entirely pipeline visible, including, but certainly not limited to, shipping a trivial markdown parser to the browser instead of doing the conversion on a server.
In a perfect world, the browser should have simply provided something like canvas hooked up to something like WebAssembly, and we should have provided for everyone a trivial markup file format rendered that people could include by default and a handful of graphic file format implementations that could be easily mix-and-matched to pull just the ones people wanted into their site.