Provided whatever game mode had a spotlight in the news which explained what it was and how to play it, it could encourage new players to try it out. For example, I've never played a phantom game (and have only seen a couple of casts of phantom games) so I'm put off joining one as I'd be relatively clueless and probably face alot of anger from the players when I play badly. Similarly I won't even consider various other mods since I've little idea of what they do.
I expect it would in part come down to how it's marketed/pitched - if it's promoted as something for new players, to let them experience different types of game modes in a non-competitive setting, with experienced players encouraged to be helpful and play for fun, I suspect new players would be more likely to queue into it.