SOA Fable: Can you handle the pressure???

One of my friends had this experience in recent past, which relates to SOA.
He had his storage boiler system replaced with a combination boiler. A storage boiler system, heats the water and stores in a container to be distributed on demand. Whereas the combi boiler does not need a storage tank for hot water. It directly connects mains to all taps, heating the water while its flowing thru the boiler. So it supplies hot water at mains pressure. The combi boiler is very energy efficient because it heats water only when needed and does not waste heat while hot water is stored. There was an unintended consequence of this introduction of efficiency. Till now all showers were shielded from mains pressure by a storage tank, but now all they were exposed to mains pressure. Within short span of time, all his showers broke down because they were not rated to work with mains pressure. He had to replace all his showers to work on mains pressure.

What is the relevance of this tory to SOA? In SOA, services are introduced in an evolutionary manner. We cannot design the entire enterprise in one go for services usage. We keep on introducing the services as and when we can. Service consumers too come on board, as and when they can. It means that overall configuration of system in terms of service suppliers and consumers is very dynamic. So you are not sure what non-functional change you will be exposed to, as a service consumer. If a upstream service were to become more efficient it might mean additional workload for downstream services. How do you handle such an upserge in demand?
The key is to be prepare to accept unprecedented demand. SOA is desirable but not EASY....