I think this is a problem better solved by a smarter "Most Recent" page than through a whitelist.
I propose the following counter-solution.
Rename "Most Popular" "Hot maps"
Rate maps by number of unique plays on said map.
So, a Gap of Rohan game has 8 players, so a full game of Gap of Rohan gets a score of 8.
Each time its played, while full of distinct players, it gets another 8 added to its score.
If the author of the map is one of the players, subtract 1 from the score for that game so that people can't artificially inflate their scores by hosting their maps. Hosting still increases the map's score, but at least you're requiring other people to commit to increasing its score for you.
This score should only affect maps which have been chosen by players. Score should not be gained through ladder (1v1 or 2v2) since players aren't actually choosing those maps, those maps are being forced upon them if they want to play ladder.
You might want to normalize by player count, dividing the 8 by 8 to get 1 score points for a Rohan game, but don't do that. Maps with more players tend to be more difficult to fill. They take longer to fill, are more difficult to make from a map design perspective and if they're getting played despite taking longer to fill, they deserve the extra score they get.
This will get you a "popularity score" for each map. You'll have a problem with this, it will only show Gap and Dual Gap and Astro variants because those maps are constantly played. New maps will have no chance of ever making the front page.
To combat that problem, introduce a second score, and have this second score start equal to the square root of the map's popularity score (have to sqrt or will take forever for any non-uber popular map it to make the front page), and cut it in half whenever its been on the front page for more than 5 days (5 full days being on the front page, be careful coding this, if you make it 5 days since it hit the first page, and the map gets bumped off the first page by another map, you'll have cheated that map). That should force the most popular maps off of the front page, but they'll be able to return periodically (as they should, they're "hot" maps) as once they've fallen off the page they'll begin to accrue points again, building until they make a return visit.
There is an advantage in putting hot new maps up alongside older loved often played maps, it will make people associate that new map with those older uber popular maps, which increases the likelihood that they'll be chosen for a game.
Since the purpose here is to give solid newer maps the recognition they need and deserve, you must give newer maps "bonus score" so that they accrue points faster than older maps. That's how we ensure that newer maps that aren't played often make it to the front page along with old favorites. Newer maps won't have name recognition so it will be harder for them to get played.
Giving them say an additional:
-
x16 points per played game for their first month,
-
x8 points per played game for their next 2 months
-
x4 points per played game for their next four months
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x2 points per played game for their next eight months
New maps get a handicap that lasts for 15 months by this system. Tweak it to fit your taste. If you feel not enough new maps are showing up, double the multipliers. Eventually you're going to find something that gives you a really nice mix between exciting new maps and popular older maps.
This will give newer maps a nice score boost which will hopefully be enough to push them onto the front page past older more popular maps like Astro which will continually and quickly make laps to the front page as they're played over and over again.
That system may need a little tweaking to get it to do exactly what you want, which is provide players with an objective list of good maps where great maps make periodic return visits but don't completely drown out solid new maps. That said I think this makes a lot more sense than a whitelist... which I imagine is going to piss a lot of people off and cause you a lot of headaches in the long run.
The functioning of the "Most Recent" page is just not a good reason for creating a whitelist.