I'd like to see a clone stamp, but like most things in Black Ink, something a little different... Not as a brush type, but as a color-source type. So like in PS and others, you specify an area (and possibly a layer, so that the source is specific to what is on that layer, and then you can clone it around the current layer, but still using the various modifiers of the current brush.
Basically no different from using an image as a color source, but in this case, the 'image' is the offset coordinates from where you are painting currently (possibly from a single specified layer not just the cumulative layers currently visible).
If you go to a lot of trouble of outputting the current image and then bring that back in as an image source for the color input, and then continually reposition it in lieu of Control-clicking like you do in PS, then you can do it currently in Black Ink, but you may also have to repeatedly save out the current image and re-select it as your new image source to get the same functionality. Easier if we could just control-click on the image.