So long as all these experts are doing is writing
critical reviews,
the need to strictly limit who can and can't write such reviews is
overrated. If, on the other hand, you want to give these experts the
power to enforce their suggested changes, then you're fundamentally
changing the structure of Wikipedia and you might as well fork off a
new project to do so.
I wasn't thinking of critical reviews or suggesting changes, I was
thinking of them vouching for the accuracy of the article. It's not
for our benefit, it's for the benefit of readers. If the readers can't
be sure the expert is really an expert, then there is no benefit.