Even if you are not a newbie who wants to avoid pvp situations like some here suggested, shatter is the best way currently if you are just after the mounts, so even clever people will just queue shatter if they wanna farm 3 mounts at once instead of only 2 with the old modes. Let's say they introduce a new pvp roulette with just 1 mode for a week, if they don't restrict the other content like shatter during a sealrock week, I doubt it will flourish. The majority still just selects shatter and doesn't care. WoW increased rewards for 1 battleground for a week if I remember correctly, that could work out maybe compared to a 1 time roulette bonus.