Originally Posted by
Murderdoll
Think of it as Greater Rifts in Diablo. You can keep scaling up the difficulty of the dungeon trying to push harder and faster.
Its going to be one of those things where if you want to push for it, youll be taking a set composition.
If you want to group for one with pugs you wont be brought if you arent one of those composition.
If you arent in that composition and youre just interested in doing them at your own pace, youll need a guild group or get lucky in the group finder (I know on Frostmourne for example, you will be hard pressed finding a group if you arent in that "best comp" group).
Elemental has already been shunned to the Do Not Invite list on beta as has SPriest. Thats not to say they wont be able to do them. Youll just need be probably find a guild group and you probably will have a hard time pushing for those top levels in a timely manner.