If you think about it, the forum has already changed a lot since its inception. If you check this Bitcoin Wiki piece about the forum, you will learn that it wasn't always Bitcointalk.org. Looking at a few sources, it seems that the original URL was this one > http://bitcoin.sourceforge.net/boards/index.php. After that, the forum was moved to bitcoin.org. Now we have Bitcointalk.org, so the forum has already seen it's fair amount of changes. Another upgrade to a more modern software wouldn't hurt the forum or its importance.