Hopefully it's self-explanatory. The frequency at which the notification takes place will need some attention as a 6v6 with this thing chiming in each time will be frustrating. I, however, think it's very necessary.
Time and time again I'm sure you like me have been part of a team game where an ally is under attack while you yourself are concentrating on managing your own army/eco. Unless you are playing in mumble/Skype/Teamspeak (loser-ville)/etc it can sometimes be far too late to send help or even recognize that your ally is in trouble.
This - I think - is critical in getting team play steered in the correct direction. It's far too difficult to get a "mumble stack" if you will all the time on both teams so most people are okay with playing with randoms. That's fine and all but it's kind of difficult to type while under pressure...