That might be going a little far. Adding an extra-large size to a listing for a T-shirt (for example) shouldn't invalidate all of the existing reviews.
A more targeted approach might be to disallow sellers from adding variants to products which are not currently for sale. I suspect that would cut down on most of the abuse.
A more targeted approach might be to disallow sellers from adding variants to products which are not currently for sale. I suspect that would cut down on most of the abuse.