The only thing that your really suggesting is allowing Plus! to place a floating contact item on the desktop when the contact comes online or whatever.
Plus! can play sounds for an action but not as your suggesting it would play one for all of the above.
Whats so special about this? Plus! can already do it... Right Click a contact in the Contact List > Messenger Plus! Extras > Notifications
What I am trying to say is there really isn't anything different in your suggestion from the features already in Plus! all your doing is categorizing them into a feature. Although I do admit I like the idea of the Contacts on the Desktop when they come online the only thing is Patchou probably wont do it because of the way they are placed on the screen it could cause problems if say all your vip contacts come online at once and you are bombared with floating contats.
Sorry to burst your bubble but it probably wont be added.