I've had an idea like this in my head for awhile now. One use case, you're at home and something just happened, large car accident, loud noise, etc and you want to be able to chat with the people around you while sitting on your couch.

When stuff happens around me when I'm sitting at home I find twitter to be too slow to update and it has a lack of information anyways.

But then you're just dealing with the same network effects that twitter is having trouble with.