I know, this is a double-edged sword, but personally I would prefer it over having to change lobbies/playlists to play DLC, and then only being able to play the DLC maps and nothing else.

For me, DLC MP maps are supposed to bring variety, but separating them into exclusive playlists creates the actual opposite of variety, since you can only play the DLC maps (mostly not more than three for a game like this) and nothing else. Which creates monotony even quicker, and people are then forced to change lobbies in order to NOT play the same three maps over and over again.

Ghost Recon Future Soldier did this perfectly, I think, and Halo 4 did a decent job as well, and it should be noted, that the "only DLC" playlists in those games were the ones with the consistently lowest population. For GRFS, the playlist with that integrated all DLCs and the on-disk maps into a even rotation was consistently the one with the highest population.

For each new DLC they should add a new "playlist":
You can either play only on the on-disk maps, on disk-maps and DLC1, one disk-maps and DLC2, or on all maps (disk, DLC1, DLC2). The chance of getting a DLC map to vote on should be 1:2 in the first two weeks after DLC release, then 1:3 or 1:4 once the novelty has worn off, and all maps should be played eventually in the course of continuous matches of the same lobby.

I understand that when you buy DLC you want to play it, and I know that in games that integrated DLC maps into the regular rotation, the first few days people would quit if a non-DLC map came up, but to counter that, DLC should come out before the on-disk maps have grown stale. And if the map selection would make sure that the DLC pops up frequently at first, then less frequently until they became "just another map", I think that would maximize the variety and enjoyment you get out of DLC maps.