In regards to ratings, one thing you may want to consider is that ratings across the board are now higher since the patch where the ratings box was set to default to unrated. Before that an average rating that was a sliver above 4 stars was near the top. Meanwhile top ratings are now closer to 4.5 stars.
The problem is that older established missions have a deep reservoir of reviews that took place under the older, less generous system. All of the default 3 star reviews reduce the rating of those older missions, making it so they can't really compete on equal footing with the newer missions that never received any default 3s.
If nothing else there is definitely a strong incentive for an older mission to be copied and republished to get a blank slate.
My personal recommendation is that only the last hundred reviews be counted for the top rated list. This also would have the advantage of making the top rated list less static. To stay on top a mission would have to continue getting good reviews, so it cuts both ways. Maybe an older mission was once considered great but over time it has been surpassed, it shouldn't remain on top merely by virtue of all the past reviews it banked, and by the same token it shouldn't be penalized simply for existing during an era where average scores were lower.
I'll wait to see it before I complain but this sounds overwrought and just shifts the problem elsewhere. The search feature is what needs fixing, not who gets to be on the top of a sorted list. I don't see this helping at all; and will indeed make the list even more static.
I am reserving judgement until I see it work but, as a betting man, I am calling disaster.