I reckon nobody takes the Academy seriously anyway so we're safe 😏

Eh, that's got flaws too.

It isn't like you don't end up with some degree of centralized organization, or at least with a central core of contributors. That in itself isn't a nice I obstacle, but if that core group ends up being core because they're willing, rather than capable and good at the job, that becomes a giant problem.

At least the OED can be said to be handled by people that know language, and English in specific.

Besides, as soon as any dictionary becomes used by enough people, it becomes an authority. That's unavoidable. Open sourcing doesn't prevent that, and then you'll still have people treating it like the dictionary is the authority rather than being a repository of language as it exists and changes.

English doesn't have regulatory body proscribing what is and isn't allowed. Every major document dictionary, including the ones mentioned here, follow the changes, they don't force them. The reason they're authorities is the long time they've followed language successfully and in timely fashion.

The real importance of a dictionary isn't private vs open, it's the skill involved in writing the definitions. That takes a good bit of work to develop.