Gameplay concepts that I generally like to see are:
  • Fast gameplay with a significantly reduced GCD
  • Multihit attacks
  • Swords/Greatswords
  • Spellblade effects
  • Time magic (especially when used to rewind time or alter action recasts)
  • Teleportation
  • Shapeshifting
  • Weapon summoning/Armiger
  • Counterattacks
  • Debuff management
  • Interesting movement tools
  • Hitstop animations
My ideal job concept would probably be a Striking Melee DPS based off Final Fantasy Tactics' greatsword users, like T.G. Cid, Agrias, or Meliadoul. Link the lore to the Corvosi Unyielding Blade sword style, with a mix of Mystic Knight style blade enhancement and Ivalician spellblade effects. Add in Celes' Runic and Leo's Shock for good measure. And none of this greatsword with cutlass handles or spikes nonsense - just a traditional, clean, double-edged classical medieval sword in the style of Defender and Save the Queen. Fusion sword concepts are fine too, as long as the core weapon follows a more traditional design.

The other job concept that I would consider playing is a melee range healer, especially one with a quarterstaff and non-MP based resource management, but I doubt they'll ever shake things up that much.