You're intimate and have sex with your wife. Do you do the same with your "work wife".

Your wife is--or should be--an equal partner in your life and relationship. Is your "work wife" an equal partner at the same level in your business? Make the same salary?

If an executive needs an assistant to which they can delegate tasks and who can shield them from the mundane day-to-day stuff, then just hire one and call them that.

The whole "work wife" thing just adds a bunch of connotations that are unnecessary and complicate matters.