Title says it all again, 

It would make it more convienient in contacting your criminal gang, and allow you to spam everyone if they take forever to join :D.

If they take forever to join, I'm assuming it's because you sent a blind invite and didn't contact them in the first place to join you? This is a feature that isn't needed if you take the time to get your crime group settled in the first place. Sending a mobmail upfront could save you the agony of having to wait for 20 minutes to see if someone joins you. Just sayin'. :)