In the last OOPSLA Linda Northrop gave a talk on Ultra-Large-Scale systems (ULS). ULS introduces a lot of unprecedented challenges. An ULS is basically a system of systems each of large scale itself. Consider the Internet as one possible example, especially when you combine the Internet with Pervasive Computing. There are a lot of issues to be taken into account for such system. One example is the human interaction which will definitely be part of those systems. Linda motivated the problem we face with such systems with the metaphor of building cities instead of building buildings as we do today. How can architects cope with such systems? From my viewpoint, the development off ULS systems will be driven by emergent behavior and a mixture of system/software architecture efforts. By emergent behavior I address the problem that it is simply impossible to anticipate all networked entitities, especially when we consider continuous change. Thus, we can't come up with a fixed architecture. We are entering completely new areas here. There is no chance to really foresee now all the implications of an ULS on software architecture. However, we will need to introduce software/system architecture principles and guidelines that should impact the architecture. In addition, we will need to come up with some core components such as repositories, persistence stores, other kinds of central services that are essential. Everything would be initially driven by typical workflows that should happen in those systems. Essentially, we will need to start simple. Use simple abstractions and principles that can be combined to more powerful structures. The human brain is an interesting example as its main constituents are rather "simple" while its overall behavior (i.e., emergent behavior) is incredibly complex. One should keep in mind that it took mother nature millions of years to develop those brains by constantly modifying, enhancing the design, even removing old design that didn't work, until today and beyond. That implies, that we won't get it right in the beginning. Thus, ULS development will definitely need experimenting and playing around with concepts and configurations.
Swarm intelligence was a sort of precursor in that direction. Define behavior of entities as well as their interactions locally and then let the system act globally. The killer application were ant populations.