Good idea, but if you do that, I would worry about the quality of reviews...people typing anything in the review box just because they want a new chapter. If it's a review like 'update more' or 'nice' then that sort of review isn't worth having...well, not for me anyway. :/ Maybe specify that they have to be 3 reviews of good quality, even if they give constructive critique.
Hmm, that's a good idea. I'll have to make sure I say that. Tbh, reviews that are just "good job" annoy me. >_<