This has been discussed before. It isn't going to happen. The next major update to the forum software (besides security bugs) will be the new forum software.
I am not sure how hard is to update SMF but if that process is not something insanely problematic maybe forum crew shout try it?
It is in fact very hard. Theymos has made numerous security changes into the code and other features such that it would be very difficult to port the changes over and ensure that there are no new bugs introduced and no new security issues introduced. Note that these changes are not plugins but rather changes to the base SMF itself.