Most forums already have this, hell even phpBB recently added this into their platform.
I guess this could tax the servers a lot more however it will bring more activity to the site (not that it needs it).
The last time I have seen a feature added to MMO-Champion is, well, never. I understand testing, security and performance are all vital however plugin which will make the whole UX much smoother is relatively safe and usually bug free, considering its so widespread.
I think it's rather important to keep up to date with web technologies. No one is asking for Facebook 2.0 however little improvement on the UI/UX part would go a long way. There a lot of easy, little changes that could be made to MMO-C to make the overall look and feel of the site more up-to-date (Notifications arent one of them, its a bigger job ofc).
Thanks,
K