I'm not sure what reason is valid enough to warrant Team Snipers not being implemented into the Hardcore varied playlist. It's very competitive, takes skill to compete highly, and fun to many in the Halo community (based off population).
It would easily be #2 in population if created. It would surpass MLG, Objectives, Squad Battle, and Doubles handily in my opinion. It's proven to be highly populated before, and I can't see why it would change. To not make it a ranked, permanent playlist because it will take away players from Social Slayer, Team Slayer, SWAT, whatever is a truly ridiculous reason, if true. I thought Bungie wants playlists that will capture a lot of matches and players, not ones that have minimal players and just load up space (having two Big Team types, for instance). Team Snipers will assuredly bring in tons of players and games.
Creating new maps for Snipers still hasn't existed, unless they changed things so subtle I didn't recognize it. They changed the maps for SWAT and Squad Battle -- MLG I do not include because MLG themselves created it, but for basis they still use the variants. Certain maps should be edited for spawn starts (ie. in Last Resort where you will directly be looking at the opposing team from the get-go) and added or changed up equipment.
I don't see why more map changes are used for specific playlists anyways. It was done very often for Halo 2 and I think it would make certain playlists and gametypes more balanced and fresh.