I want to see either a savage-lite version of 4 man dungeons or the current version of 50+ dungeons being made into 8 man version and kinda getting a savage treatement where we see new mechanics and such from normal mobs/bosses(expert dungeons is a joke in terms of difficulty). It doesn't have to be as hard as savage since your going through multiple bosses, but i do want to see actual dungeons at end game and not just boss fights. 24 man is the only time i feel like we get this type of content and i would like to see more in the form of smaller groups.
Edited 2/15/18:
So my idea overall:
1..Higher level gear that is limited like weekly tomestones like how alliance raids give tokens.
2.Give weekly tomestones like any other dungeon just slightly more.
3. High level version of farming for crafting materials,glamour,possibly mounts,materia,etc.(Since it would be more challenging the rewards will be harder to obtain and therefore it will help control the market.
4. Trash mobs would have significant more HP and be more dangerous and maybe have one or two abilties that are similar to a raid mechanic.(Stack for split dmg, tethers to other mobs, prey, charge ability with prey(t10),etc.)
5. Special treasure chests would drop with temporary bonuses like extra time,attack power, defense,re-raise effect(to automatically raise players once if they die that last until used) higher quality treasure for next boss chest opened.
6. Treasure Chests would have multiple tiers(bronze,silver,gold,mythril,etc) to make certain materials and materia more rare to control the market and make it worth doing multiple times to keep population for this possible type of content or roullette high.The further you get in dungeon you far more likely to get upgrades to your treasure through normal mobs.
7.Quality of treasure is also based on how times you wipe on a boss, bosses won't have enrage and be more forgiving so you usually only wipe due to boss mechanics.However bosses will still be pretty challenging. but since there is no enrage you can still save a fight no matter what no matter how raises are thrown out which will make things more interesting and you only truly lost when you given up or have raisers left.
8.Final bosses will obviously be way harder than previous bosses in dungeon , and will drop very good high quality materials and gear, but will drop more chests,gil,and special items like mounts and whatnot based on overall performance in dungeon and just particularly on this boss.
9.The biggest enemy is not any boss or mob, its the timer, with no enrage for bosses it is really a matter of racing to the finish and getting a clear moreso than spending 30 tries on one boss, as long as you can keep your party up you can eventually beat them. I think it would be a interesting balance and be very similar to how 4 man boss format is but a savage light version.
These are just a few ideas that could make these dungeons more challenging but there is things in place to make things easier as well as upgrades that are similar to pomanders from palace of the dead and whatnot to edge things in your favor and undo losses(make treasure quality higher). These are just some of the things i think would make a unique and interesting experience and not just another dungeon run. Think all the 50+ 4 man dungeons could easily be retooled for this purpose in a interesting way, and even though the content would being reused there is enough new mechanics and approaches and things worthwhile that i think people would still very much enjoy it.