Yes, actually the playerbase has been asking for a mail system for longer than we have been working on the engine...thanks for pointing that out. Being focused on one feature to the degree where we ignore all other "old" requests or issues is not how the current team will be prioritizing the future.
Macrosun is a game coder...not a render coder. It is likely that he could help if he wanted...but it isn't his area of expertise and certainly not an area he is interested in. Sort of like me taking the time to type up yet another "different people do different things" thread (at this point I have done this so many times I suspect this is a running joke on the forums..."lol...we got Means to explain it again!1101010!"). If Macrosun had been tasked to only the engine there would be NO: Social Tab, Raid Instances, Raid Interface, Instanced Cities, Mail System, Knockback, Fear, Mindcontrol, and countless exploits and crashes and bugs would still be in-game.
Is the engine taking longer than planned? Hell yes. Do I regret any of the choices that brought us to this point? No. I'm VERY happy we have been able to continue working on this at the right pace so that we can deliver what is best for the future of AO. If we had thrown 30 render coders at this a couple years ago it would have been done...but it woudn't be close to as good as the result and support we are going to get when this is finished.