>> For example, typing 'C-x v L' (vc-print-root-log) outside of a project
>> displays the minibuffer with the prompt "Directory for VC revision log: ".
>> It should provide a list of the default values from the project list
>> saved in ~/.emacs.d/projects
>
> Note that one would have to verify that each directory in the list is
> a part of a VC repository.

Maybe something like: