I just don't see why it matters if someone necros a thread. Or at least why it matters enough that we need a special rule or change to the site. I mean sure it's dumb but there are plenty of even more annoying things they could be doing with their time.
If people start having a discussion in an old thread then..well guess what, it's once again an active thread that people are interested in. Otherwise just scroll past it like you would any other thread you're not interested in.