Currently mobile links are shortened as mobile, but it would be useful if they could be treated has non-mobile by default. A non-mobile link is automatically redirected to mobile and the reverse isn't true, which makes more difficult to create universal short urls in mobile.
For example, https://meta.wikimedia.org/wiki/Special:UrlShortener?url=https://pt.m.wikipedia.org/ should give a short url for https://pt.wikipedia.org/ .