I don't think that's what he meant. If I am understanding correctly, he meant that other sites would begin trying to offer signature campaigns externally which lower ranked members could join.
For example, someone could go on one of the several other Bitcoin forums on the internet and say 'I will pay you xBTC per post for putting my link in your BitcoinTalk signature'. This would cause exactly the same problem, apart from this would be more difficult to moderate.
That might very well be true. We can't control that, nor do I think anyone on this forum is concerned about signature campaigns popping up on other forums--that's not up to those who would flee from BCT, is it? It's up to whoever runs whatever forum(s) you're speculating about.
We are speaking of our concerns for bitcointalk.
And I strongly think that nixing lower-ranked members from campaigns would help. More moderation certainly would help too, but I think we ought to try the restrictions and see what happens. Kind of like an experiment. Then at least we'll know, right?
I like the idea, and think it's worth to give it a month or two time to see what it will do with the total junk that comes from these lower ranked members. It will also give people something to look forward to in the way of these lower ranked members to build up their account with decent posts so that they can finally reach the level that is allowed to join a campaign. And those who from these lower ranked members keep spamming with junk anyway, banhammer. Simple.