Since we are getting only 2 drex dungeons for now it would be worth for them to take time to develop extra dungeons like the one proposed and that others have(me included) suggested in the past as well. It could be just one extra such content each major patch but if it's done right it could last for a while. And the rewards they can set to be scaling like the island exploration stuff where rng can drop you stuff up to i210.

It could drop some tomes but primarily it should be there for those that want the adventure. The impatient crowd will still get 2 dungeons they can spam that are run through. But I want some content where I can go and spend time with friends exploring, figuring stuff out etc...

They call them island exploration I'd call them just explorations - and they could be anything really - basically instances you can explore in. Have them be challenging or easy or random. Co-operative or just soloable, light or full party. Mix it up. Ability to swap jobs and such.