Seems like a good idea. Not only should the reviewer have played the game for an extended time, there should also have gone a significant time after the game's initial release.
Poor early reviews should be altered if bugs are fixed and/or new content is provided some time later.
Likewise games that are fairly good initially may nowadays become plagued with in-game purchases and generally worsen over time.
What review mess? Let people speak their minds. If they want to bash devs when they think devs do bad things, let em. Not that this change really affects that at all btw.
The only reviews that should be "cleaned up" are those regarding individual technical issues unrelated to the game, or those that don't elaborate. Maybe set an input minimum. IMO, negative reviews seem to be increasingly justified, due to trashy development and production, where profit is the goal instead of art-form. (ie. FC5, Wolfenstein Youngblood and Rage 2). Everyone wants a good game