Volimance says:
Someone abusing that function is probably going to be abusive in some other way (is my guess).
This was a consideration as well; by in large a lot of my decisions about features came in early into the site development, when people weren't yet really here, so most of it was erring on the side of caution.
How I see it, if implemented, you can see when a personal was last active via timestamp, which means a GM or player who sees a lack of action can prod a player to post via PM. The big concerns I see for this are actually with planned features/fixes: when I get the PM emails working again, if a GM sends 5 PMs in 20 seconds, the user will be a bunch of email. But I guess I could also limit how many PMs someone can send per time period (which means more dev time for me). We've also discussed a ping system, something typing @Keleth to get my attention in a different search field. My current plans for that feature do not involve emailing the person on every ping, but rather having a different forum search notifying them of an unread thread with ping in it. But this could mean that if abused, the ping system would need a lot more work and thought.
Mind you, ANY new feature/change involves work, so that shouldn't be a consideration, rather how much work for how much we get out of it.