Here’s the short version of Torvald’s thoughts on GPL2 vs GPL3:
“To say that GPL version 3 is like GPL version 2, only better , is decidedly wrong as GPLv3 is very different from GPLv2.” – From a Q/A on GPLv3 in 2014.
Note that he isn’t saying GPL3 is a bad license, just that it does not serve the same purpose as GPL v2, so calling it v3 is a misnomer. It is similar to the GPL vs LGPL divide. But even setting aside that the FSF changed the nature of the GPL from version 2 to version 3, if you open the door to all future versions, you rely on the FSF not changing its own nature at any point in the future. That is a gamble with what benefit? Saves you issuing a statement at some future date saying “all my software previously released under X license may, at the licensee’s option, be licensed under the X+1 license”. Meanwhile, if the FSF gets bought off, the V4 license could read “All rights reserved, redistribution prohibited” and you’d be screwed.