Not a terrible idea as long as 1) it can be declined freely and without penalty, 2) there is a "be available for conscription" toggle that can be changed at will, and 3) it can be completed an unlimited number of times per day if desired. I don't think it's a great idea, mind you, just not terrible.

I think it would be better to instead expand the queuing system to accommodate queuing for multiple roles concurrently. Alternatively, queue times would decrease if roulette rewards could be applied to any class, not only the class used in the instance. I'd be more than happy to do my roulettes as a tank or healer if I was allowed to funnel those rewards into whatever dps class I was leveling at the time.