The question is: how does a toy language like wiring become useful for prototyping of real applications?

The answer I’m proposing is to use the wiring diagram as a skeleton on which you hang all the other coded bits written by developers. I’ll be deriving that model soon.

Yes, it is probably accessible to non-programmers.

Does it scale? (yes; you will see that)

Once you try to do anything realistic, it loses its simplicity. (Solution: the Anatomical Application Model)