[jmull]

It's saying switchovers, when refactoring a system, can be hard, with a big risk of unforeseen complications.

So identify as narrow a case as you can, implement that first, and once that's good, build out from there.

That is, break down your problem into manageable chunks. Nothing new...

the part that might not be obvious (there are many ways to break down a problem, after all) is the idea to fully deliver a narrow case.

Seems pretty reasonable to me.