The downside is that not every author is a good person. I believe that a lot of people will abuse this feature. I'm not saying you are going to abuse it, nor am I accusing anyone on this forum. But I've seen authors on main site, that don't visit forums, doing questionable stuff. And this is only my opinion based on nothing, but I don't believe that there are more honest authors, than authors who chase after money and fame. This will help them a lot more than it will help authors who won't abuse it. Remember that thread when someone wanted a dumb protagonist tag? Are authors with dumb protagonists going to use it? Same here. Will majority NOT abuse this feature? I think it will be abused.
There is a couple more points I want to say. If the review is truly completely misleading or a straight-up lie, you should report it. Report it, state why it's wrong, give some evidence, and I believe Tony will delete it. Another point is, some reviews are prone to change. Yes, it's a very tiny amount, but some reviewers change their reviews, depending on how far they've read. Lastly, you can PM the reviewer, and politely ask them to change the review, if you believe that the reviewer made a mistake.
But this is only my opinion, and it won't decide anything since I'm a minority in this case. Anyway, it's Tony who makes a decision. If vast majority wants this feature, you will probably get it.