In reference to the article in the provided link using twitter as a public announcement system is an interesting advance. It does open up the possibilities of Twitter as a stateless Low QoS message bus.
Twitter will need a few extra pieces of function in order meet the demands of these public services e.g. message by provider, location, area, town, country, user etc and by device - pro, friends, anonymous, government etc which will bring in security reqs. Some comments to the article talk about adding sensors to tower bridge. Thjis technology is provided by SCARDA devices that publish events through a message bus to some other system - this technology is common umoung oil pipelines for measuring flow rates across the pipe network.
It very interesting to see public consumer messages converging with enterprise messaging s0olutions.