I personally don't see this being a good idea. Giving literally anyone the ability to create new lore or change existing lore would just make a huge mess. Especially seeing as how a lot of Thaumcraft's lore is open to speculation. There's been a lot of theory-crafting here over the years because of that. It would be better if someone just made an open source addon instead. That way you know all the content is non-cannon right from the start.
Even in OSS projects, "literally anyone" does not have the ability to influence the official project if the owner does not wish them too: If they want to submit content it has to be via a pull request that the maintainer of this archive will review and accept.
They *could* branch the repo, and make their own version of the mod with their own content. But that would not be part of the default thaumcraft download.