I had a nice moment thinking about the loss of multi-bloodlusts and stacked ToWs... The world was indeed going to end.

My personal opinion is that the worst transition for multiboxers has already occurred with the launch of WotLK. Pre-WotLK, area of effect damage and AoE crowd control was far less common than it is today. The addition of strong AoE abilities to almost all classes really hurt PvP multiboxing and caused several interesting group compositions to go away. (e.g. 4x/5xHunters). PvE 5-man content hasn't changed a whole lot, but the same can not really be said for raiding. Boxing in raids is just not as easy at it used to be... I recall bringing 2-4 shammies into Karazhan to help fill out my guild's group as needed, but most of the raid content in WotLK hasn't supported easily bringing in extra multiboxed characters. (Mad props to those who have pulled off raiding, though!).

We've proven that the multiboxing community is pretty adaptable and will roll with whatever changes hit us. I think the expansion will be great fun, personally. Rated BGs has excited a lot of folks, myself included. It seems like the perfect boxer playground!