I'm not advocating migration to a mainframe as much as I'm advocating the mainframe is a platform too. Transition across platforms is more difficult than expansion of the same platform, but in planning for growth there might be a scenario where the move across platforms provides a more desirable result then just adding more platforms. In that case, the migration will have to happen, and redundancy will have to be there to insure continued service.

You may not be looking at such a scenario. But take a real world example of a large local bank in a closed in a somewhat isolated society, which strategically wants to deliver financial services to the world. They know they need to provide 7x24x365 availability to be successful. They have areason to consider moving to mainframes and running the fastest db they can get their hands on. And that is what a handful of China banks are doing as they break through the isolation and begin competing in the world market. I've heard rumor that they will have the largest IMS deployment IBM has ever seen. IMS is one of the oldest manframe database but it is the fastest, and those who need to process transactions at breakneck speed are using IMS.

If the rewards warrant it the risk will be managed!