As uninit does not need to actually write out any data, just remove it, it should be possible to uninit in old stores.

    % git annex uninit
    git-annex: Repository version 2 is not supported. Upgrade this repository: git-annex upgrade

If the repo happens to be broken, this essentially locks in data.

> No, because you can always check out the version of git-annex you need
> for that repository.
> 
> uninit, as implemented, runs unannex on every file and then does some
> cleanup. The cleanup does not need to write state, but the unannex does.
> And it depends on the object directory layout, which has changed between
> versions. So supporting old versions in this code would complicate it
> quite a lot. I don't want to go there. --[[Joey]]