GPLv4 could be the MIT license. GPLv3-or-later is a statement of arbitrary trust towards the FSF. Corporations serious about licensure, like SixtyFPS, aren't fans of that. (I don't think I've ever seen GPLv3-or-later in the wild from non-GNU/FSF software.)
GPLv3-or-later is pretty commonplace in the world of free software even outside of GNU stuff.