The basic idea of Domain Event Driven Architecture

I am interested though in hearing about how this kind of inter-application communication could evolve into a more well-defined protocol.

REST has become a fairly well defined way for applications to communicate, but it's pretty much geared toward a request/response model.

What's being described here is more of a pub/sub pattern, but to my knowledge there are not any agreed upon standards that publishers can/should use to format event messages and identify objects.

It reminds me a bit of the atom activity stream spec actually, which is really for publishing event streams for "social" objects:

http://activitystrea.ms/spec/1.0/atom-activity-01.html

I don't know, I think it would be interesting to see something evolve that was more generalized for application communications.

This only works for the correct set of user expectations. If the user expects the whole suite to act like one big app, then this will not work. Also, there need to be standards so one can be sure of object identity. If the web piece announces that "John Smith" has changed his subscriber level, there better be a scheme to ensure everybody knows which Mr. Smith this applies to.

This is a great pattern! I wrote a related post a couple of years ago: http://billschofield.typepad.com/my_weblog/2008/07/events-vs...

There's lots of research in this sort of area through publish/subscribe and knowledge-based networks. Have a look here http://kdeg.cs.tcd.ie/KBN

Isn't this how most complex event processing (CEP) engines work?