I think it will work as long as authors understand that the review might not be glowing
If I might offer you a bit of constructive feedback, I am not sure how many authors who claim they want to be huge successes realize that this is actually a *business* (if making money is the goal, it must be) and that serving the *customer* is the most important thing. For example, you claim you only post positive reviews and that is great for author ego purposes, but it does make you a bit less trustworthy a source for a customer legitimately trying to evaluate a potential purchase. I know personally that I have seen books on Smashwords with only glowing reviews and then I read a sample and wonder what those people were smoking
It makes me feel like the author had only their family members review it or something, and that's total amateur hour. I immediately cross that author off my list of authors to watch.
I think a review service like the one you suggest is a good idea, but I worry that in trying to serve authors in the way you are, you are not serving readers, and that will *hurt* the authors you claim to be supporting. If I am a reviewer and I participate in your service and my review does not get posted because I don't give the book five stars, that will be the last time I participate in it. Imho it is much better to post balanced reviews that help guide readers toward appropriate choices.