All four together would be amazing, but a lot of organizations aren't ready for this. Moreover each technology has its own set of tools and platforms, and its own set of disciplines and disciples.
In Betting on the SOA Horse, Tim Bass describes this potential synergy using the language of gambling - exacta and trifecta. I'm not very familiar with this language, but what I think this means is that you only win the bet if the horses pass the post in the correct sequence. Tim writes:
"Betting on horses is a risky business. Exactas and trifecta have enormous payouts, but the odds are remote."
In On Trifecta and Event Processing, Opher Etzion disagrees with this metaphor. He argues that these technologies are mutually independent (he calls them "orthogonal"). If he is correct, this would have three consequences: (i) flexibility of deployment - you can implement and exploit them in any sequence; (ii) flexibility of benefit - you can get business benefits from any of them in isolation, and then additional benefits if and when they are all deployed together; and therefore (iii) considerably lower risk.
My position on this is closer to Opher. I think there are some mutual dependencies between these technologies, but they are what I call soft dependencies. P has a hard dependency on Q if Q is necessary for P. Whereas P has a soft dependency on Q if Q is desirable for P.
In planning a technology change programme, it is very useful to recognize soft dependencies, because it permits some deconfliction between different elements. Deconfliction here means forced decoupling, understanding that the results may be sub-optimal (at least initially), but accepting this in the interests of getting things done.
In a perfect world, we might want to deploy all four technologies together, or in a precisely defined sequence. But pragmatism suggests we don't bet on the impossible or highly improbable. The challenge for the technology architect is to organize a technology portfolio to get the best balance of risk and reward. This is not primarily about comparing the features of different products, but about understanding the fundamental structural principles that allow these technologies to be deployed in a flexible and efficient manner.
Discussion continues: Technological Perfecta 2