Teaching is a skill. An expert typist typing "the fox jumps over the lazy dog" at 30 wpm doesn't make one a good teacher.
Suppose we suppose to suppose.
An expert visiting a classroom with a competent teacher would be the best thing -- the teacher can provide direction and control over the class as well as assist with prep.
A Boeing machinist specializing in door plugs might make for a dry presentation. But a Boeing machinist specializing in door plugs who has the help of a good physics/engineering class teacher to lay out a lesson plan would probably be pretty fun.
Most of what's being taught is how to learn - and knowing how to teach is the hard part.
Also, my experience is that most experts aren't mediocre teachers, they're terrible teachers.
There isn't a degree in "Expert". How would you determine who should "teach high school for one year"?
This would cause havoc in schools as these teachers would be there for one year and then gone.
If not, what do you mean by “require”?
Also, how will the salary difference be made up? If I'm making just enough to pay for my food & rent/mortgage, and suddenly I'm working on a public teacher salary for a year, what happens to my house and family when suddenly my salary is cut by anywhere from 50 to 90%?