So that's a good thing for this forum, yes? But I doubt that if they have an opportunity to wear a signature on another forum they're not doing it--but that's another story. In either case, the argument that you're driving spammers away isn't much of an argument (no offense intended, sir). That's the point of this.
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.
I disagree that limiting signatures for lower ranked members will achieve anything, for both the reason stated above and the reason given by Quickseller*. As I have said previously, I believe the only real solution to the entire problem of spamming is stricter moderation on both campaigns and their participants.
*
I think this would only drive up the price of these ranking accounts, and drive down the price of accounts. I don't think this would do very much in terms of reducing signature spam, nor would it do very much to address the issue of low quality posts.
This is what was said about Obama-care, and look where that got us 
Regardless of political events I have no idea about, Lauda does have a point. Indefinitely discussing the subject does nothing but give it time to get worse, until it may be too late. This has been in the pipeline for several months now, I believe it is becoming fairly timely (even for BitcoinTalk standards) for something to be finally implemented.