Amazon's naive to think that banning incentive-driven reviews will make them go away. Of course they'd like to think that all vendors will transition to Vine, but more likely they'll just go underground - when they're not marked, readers can't adjust their interpretation based upon the information, nor can they be studied statistically. Vendors will also get suckered into participating in underground paid reviewing, increasing their real sales costs, and run the risk of losing the invested money when they get caught.
There's been several comments about "co-mingling" of products. I'd agree that we, and Amazon, should be concerned about that, too. Amazon could address the co-mingling issue for reviews that are connected to a purchase by identifying the vendor associated with that purchase, just as when products are lumped together, the reviews have a notation as to which of the several products are reviewed. Amazon needs to go even further, and separate the star rating average by product and vendor as appropriate. Probably, it would help identify poor vendors more quickly.