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.