Old/ current group dungeons will have entrances added to them. Those entrances will lead to a randomized dungeon that is one tier higher than the dungeon that lead into it. (e.g. T5 Deepwood Enclave will lead to a T6 Keeper randomized dungeon).
Most dungeons will have about 4 possible spawn locations for such an entrance of which one will be active at a time. We hope to ease the grind in old dungeons a little.
Now it seems like its akin to beta 1 dungeon blue portals - where you go into the dungeon and then find an entrance to go to a better pve zone.