The absence of the vertical button from the configuration is just that: We’re under the impression that demand for the vertical style of button has declined, and given the new Hashtag and Mention buttons (and large size buttons) we’ve announced today, we’ve given the space in the configuration tool over to the new models.
However, that does not mean that support for vertical buttons themselves is going to be deprecated or removed from widgets.js. It remains documented in the Tweet button developer documentation, and of course there are plenty of buttons in the vertical style in the wild.