Bungie doesnt like checkpoint abuse. Look at how abused gorgons chest is and how abused deathsinger was. That being said, i saw a glimmer of hope when i first saw trials cards. Bungie could use punch cards to denote progress within the lrison of elders. Exactly how would this work? Its simple: when in a group, the punch card system would direct the warden to start the mission at the lowest punched card in the group. So say if two of the three have section 4 completed, but the third just joined and he previously completed section 2. Then the entire group would start at section 3. This is the best way to install checkpoints within the prison of elders in a manner in which they could not be abused.