Slightly mixed about this. It IS good news overall, however I think people may miss the slightly larger picture.
Don't get me wrong I am no saint. I have used the exploit in the past for the occasional game at quite a few different brackets, primarily cause there was zero BG's happening and I fancied doing one or two on a particular char just to use it and to blow rust away. Admittedly though it was very few and far between (hence I did very few but that is neither here nor there). Don't kid yourself, MANY people are using it and some are using it very frequently. I would class it's use overall as PREVALENT.
Now certain brackets never had activity but it kept some twinks in the loop with occasional xp on games. I just hope this does not stint the activity of twinks in some of the lesser populated brackets and further compound the problem. Although the MoP changes may be good I think there will be inactivity at first as everyone levels and tries the new content raids/scenarios/PvP etc...
Of course this could force more people to get involved and get organised to queue for planned xp-off games, which of course would be great for the community. The problem is that is a big IF. I just wonder whether activity in some brackets will drop further and maybe force those people to move to more populated brackets and twinking ends up as 15-19, 20-24 and 70-74 only....
Time will tell as always but I do not have a good feeling overall with the way twinking has been for a while, and is going....