>>>> Maybe then a shorter name vc-root-dir-action?
>>>
>>> The word "action" there seems to hold no particular meaning.
>>>
>>> vc-root-dir-with-dwim-selection, maybe?
>> Shorter names:
>> vc-dir-root-registered
>> or just
>> vc-dir-registered
>
> These either sound like callbacks, or alternatively make an impression that
> only registered files will be *shown* (not marked).

Then the name could be vc-dir-and-mark-registered,
but maybe it's not needed given the below.

> Are you sure you don't want to split it into a new command that will simply
> mark a set of files you expect here? E.g. all belonging to "registered"
> statuses. That might require extra keypress, but vc-dir-root-registered is
> probably not going to have the same short combination that vc-dir has
> anyway. So it might be a wash, keypresses-wise.

VC-Dir needs the same key prefix as is provided by Dired:

* %             dired-mark-files-regexp
* *             dired-mark-executables
* /             dired-mark-directories
* ?             dired-unmark-all-files
* @             dired-mark-symlinks
* s             dired-mark-subdir-files

Then VC-Dir could provide, for example:

* r             vc-dir-mark-registered
* u             vc-dir-mark-unregistered
...

> And vc-dir-root can just be "vc-dir in the repository root" that we both
> have wanted for a while.

Finally settled with the following patch.

>> Also there is a command 'vc-register' (C-x v i).
>> Its counterpart could be named 'vc-dir-register'
>> and will open a vc-dir buffer where only unregistered
>> files will be marked.
>
> Are you sure you will remember the new commands and use them on a regular
> basis? I most likely won't.
>
> And similarly, we can add a special command to mark only unregistered
> files. Although it's usually not a problem to navigate to the first 
> unregistered one and press 'M'.

Often this is a minor problem, but given the above, a keybinding
like `* u' should be of a little help.