Yoshi-P has stated that they plan further exploration content and taking what they've learned from Eureka moving forward. This is a request for future designs that suggests a way forward that takes complaints into consideration as someone who's deeply invested in the exploratory content of XIV and it's future.
1. Three zones, three dungeons, parallel progression
Instead of four zones which require completing the subsequent before proceeding to the next with a single dungeon at the end, I suggest limiting this to three zones and placing a (24-player) dungeon at the end of each where a player only need progress through the corresponding zone to access said dungeon.
Each zone could feature a 20-level progression through the zone itself culminating in the dungeon. Moreover, the equivalent of Elemental Gear +2 and weapon (need not be relic--just an 'elemental' weapon) could be obtainable in each zone (the base pieces) and the upgrades would be parallel so that you could do each zone's upgrade separate from the other in whichever desired order. For example, hands, feet, and head could progress the equivalent of +30 elemental bonus per zone with body and legs +50 per zone and the weapon +100 per zone.
Aside from progressing to the max level of that zone to access the corresponding dungeon, these dungeons ought to be designed for 24-players to help ensure greater longevity as something like 56-players is difficult to organize publicly or privately and grows increasingly difficult to populate with time. Furthermore, duty finder/party finder support ought to be included so that multiple instances of the dungeon can be up simultaneously. After completing whatever qualifying task (e.g., Ovni) to enter, an alliance leader would go to the entrance to begin the dungeon for their group. Alternatively, single players and incomplete groups could enter the queue that lasts for, perhaps, 3-5 mins collecting players to organize into an instance. This allows both formats (preformed/match-made) without punishing one over the other, while allowing/encouraging pick up groups to organize before heading in even.
2. Zone Activities in comment below: