Concept: I realize how out of the box and highly unlikely this idea is, but I think it's a cool idea nonetheless. Since everything is about endgame now and the levels of monsters and equipment continues to rise, I thought it'd be a neat idea that endgame players would be able to get the thrill of something that will give them a leg up in the end game but also bring in old experiences of leveling yet again. The idea behind this is that these jobs are combinations of previous jobs, and improved in that the capabilities and growth rate of these jobs exceed those of older ones. Each "Transcendent Job" would require certain jobs level 75 and some even crafts level 60, which would then unlock a quest line at specific areas. These jobs would receive abilities from both older jobs, as well as unique abilities and traits of their own. However none of the new jobs would be able to be support jobs. Since most jobs that would be introduced into the game at this point would just be replicates or combinations of previous jobs anyway, I thought this would be a neat way to do it, as well as maybe try and balance the job system in having fewer endgame jobs like these. These are a couple examples I came up with, though I haven't put time into designing a structure, just a vague concept.
Valkyrie (PLD + DRG 75): A lance user who specializes in heavy armor.
Morph (BST + BLU 75): Capable of taking of forms of creatures.
Templar (PLD + RUN 75): Ultimate tank in both defense and magical defense.
Time Mage (RDM + SCH 75): Use of time to aid allies and hinder enemies.
Necromancer (SMN + BLM 75 OR SMN + DRK 75): Summons the dead and specializes in dark magic.
Choco Knight (DRG + BST 75): Using spears and their trusted ally the chocobo.
Chemist (THF + SCH 75 + Alchemy 60): Use of potions to benefit allies and harm enemies.
Engineer/Machinist (PUP + COR 75 + Goldsmithing 60): Focus on machines and guns.
Shinobi (NIN + PUP 75): Ninja that utilizes ninjutsu to make clones that fight alongside them.
Viking (WAR + SAM 75 or WAR + DRK 75): Strongest type of fighter, able to dual wield great weapons.
Spirit Archer (RNG + RDM 75): Uses magically imbued arrows to take down their foes.
Oracle (WHM + GEO 75): A healer that also specializes in unique buffs.
Performer (BRD + DNC 75): Able to sing and dance boosting the morale of allies.
Breaker (SAM + RUN 75): Heavy blade user with sword abilities to lower status of enemies.
Hunter (RNG + BST 75): Ranger that has bonded with a specific pet that aids them.
Buccaneer (COR + THF 75): A thief that is as good with a dagger as it is a gun.
Capoeriast (MNK + WAR 75): A martial artist that specializes solely in kicks.