I don't really see the point of adding this mod since all mods like this do is encourage people to make crappy non link posts until they unlock the ability to link.....either way you get spam and in order to avoid that you have to set it so high that it annoys new posters who genuinly want to participate.
Not to mention that posts with links are allowed as a first post if, for instance, the links are provided to support an argument. It's self promoting linking and other types of spam that is not allowed.
I also simply don't have time to be messing with installing mods right now.
That's the reason not to do it. As it would be a blunt tool, and could put off genuine members.
Whitney, just suggesting a change/upgrade does not put a schedule on the date to implement it. Maybe you need a tech bod who you can farm this sort of thing out to? Again just a suggestion because if something like this is found to be a good idea you don't necessarily have to be the person implementing the change.