So with the PvP changes coming with 4.0, all instances will be the same level or no level at all depending on how you look at it. That leaves the question of Frontline map selection. Based on an interview from Easy Allies, Frontline maps will be on some form of rotation, maybe weekly. Meaning that one week it will only be Secure and the next week it will be only Seal Rock (Seize).

That is one alternative to breaking up the repetition of only doing The Field of Glory (Shatter) but I would prefer if all rule/maps were available all the time, just randomly selected like The Feast.