One of the key challenges with this type of architecture is when you need to get state from the database. Clients end up polling for many real-time tracking scenarios. This presents a problem when, for example, you have 1000s of vehicles confirming state every second. Polling the database at this rate can create an overwhelming and unnecessary amount of traffic. And it doesn’t scale.
Brent Hoover's insight:
I have implemented a very similar stack on a very high volume site, instead of the Node/Websocket we used Erlang/Ejabberd which offers many advantages over the Node approach. Certainly location is still one of the big areas of mobile development that haven't really been fully exploited.