You underestimate the power of the monkeys. Never underestimate the monkey power.
I'm not sure a bracket system will work that well here. Level 1>50 is already so fast here and in 4.0 it'll be even faster since a lot of people will have the exp earring. And if you do something like 1>50 = able to sync into level 50 frontlines, it'll still be bad since most people don't care much for older frontlines. Most people just care about (Shatter) right now since it has achievements and rewards people want. When new PvP comes out they will most likely have rewards people want as well which means most people will queue for them.
I still think that level 50+ can sync into every frontlines (Or at least every frontlines from now on) is the best option. It prevents the problems of newer people or people unfamiliar with their jobs suddenly getting 30 skills at once.