Single piece flow is a legendary goal for some lean enthusiasts.
The spirit of this concept is to:

A. Align available time and unit demand to a level where takt time is equal to one
B. Eliminate the root causes of why batches are viewed as more efficient than making one at a time
C. Build U-shaped work centers which will only produce a single item without ever needing any changeovers
D. Move immediately to making batches of one and then address the rise in costs caused by the change