Comments here are disappointing. The problem with any of this is getting any momentum, so given the level of pushback, pdf might not be it. Having to be a specific version of pdf probably doesn't help. Creating new spec is hopeless as well unless you are someone very famous and can manage to get enough people to adopt. There's text/markdown mediatype which can also serve this purpose but it needs a boost from someone with some street cred. People work in predictable ways and this is a political project.
https://datatracker.ietf.org/doc/html/rfc7763