I think you're kinda missing the point that it's what they already do for MSQ Roulette. The roulette xp bonus is bigger for Praet than it is for Castrum because it takes longer. So they can for sure do it.
And you're kidding yourself if you think people are queuing roulettes out of the kindness of their heart. The whole point of the roulette system is to incentivize people for running old stuff by rewarding them for doing so. As soon as the incentive stops matching the actual investment, people will simply dip out of said roulette.
Edit :
MSQ roulette is really the best example of this. Before they scaled the reward for the roulette depending on which you got, people were simply leaving the instant they got into Praet because they felt the reward was not worth the time compared to getting Castrum.
