I think multiboxing is a symptom of a dwindling population. If all the multiboxers were banned I am quite sure it will still be just as hard to make teams for anything because the fact is there just is not enough people playing any more. And most will continue to do content within in their org or friends list.
If the population was as it were 5 - 8 years ago multiboxing would not be a problem. FC has done an appalling job maintaining this game in the last 8 years. LE and Xan additions were far to small and any content added after that is not enough to keep people interested for such a long period.
The problem of multiboxing falls on FC shoulders. they are the ones that have made the game not as desirable as other offering in the market, failed to keep content fresh and interesting. The Engine update was a massive let down for most and far to late in coming as well as the amount of time it has taken to get a few class overhauls.
Like it was said before in this thread banning multiboxers just means a few less players. I have not heard one person say the have quit because of multiboxers, pretty much all have quit because they are bored. I will concede that they have stated they won't PvP because of multiboxers though.