Only thing I could think of is adding something super shiny for tanks AND healers (Healers don't even get mounts to encourage them to do things as healer) that can ONLY be earned by doing specific roulettes a number of times. But it would need to be separated, like 200 leveling roulettes, 200 50/60 roulettes, etc to earn the item.

Now, the problem then becomes, people farm for the item, get it, and we're back at square one. Maybe you add tiers, like do 200 more of each and now said item gets a glow or something. Another 200, a bigger effect, another 200, you can CUSTOMIZE the effect.

Maybe this item is a new mount. Maybe it's just the ability to add these glows or other effects to the mount or piece of gear of your choosing, even DPS weapons/gear. This would keep tanks and healers queuing for those roulettes for the long haul. The only thing is, you have to make the rewards juicy or you still won't encourage enough people to tank and heal.

That's my idea, anyways, but would be a lot of work to implement. But we need SOMETHING to get these godawful queue times to lower.