I think it is a mistake to license anything under a “or later version” license. If you do that, you licence your code under a license that you have never read, so how can you know that it serves your intentions? You are blindly licensing code under a licence that has yet to be written! In the GPL case, the Free Software Foundation states that “The Free Software Foundation may publish revised and/or new versions of th…
Even in the worst case scenario, it remains available under the original license, and that's not going to change. What is the worst case scenario, by the way? You could say it depends on who you are. One such scenario would be for developers who agree with the FSF's strong copyleft philosophy who are betrayed by a future hypothetical revision that removes all copyleft provisions to make it no stronger than, e.g., BSD…
For example, a community could fork a project and license it under a new'er version, and then the original founder could suddenly want to incorporate the new changes but at the same time not want to use the new license, and the new community refuses request for a license to the old version. I don't think it ever has happen with a gplv2+ project, and it require a quite hostile community to begin with, but as a worst case scenario that would likely be it.