I'd like to see Role Actions removed, for starters, if they're going to remain as shallow yet obligatory. And all maintenance abilities (not spells or weaponskills) such as Lucid Dreaming, Invigorate, etc., with more, job-specific ways to affect MP regeneration and more ways to conserve and regenerate TP, TP itself reworked, or intertwined AoE and ST as not to put resource limitations solely on physical AoE.
Anything which then leaves leveling feeling notably disjointed should in turn be adjusted. Delirium comes to mind, though less than before, as does Defiance-dropping.
[Tanks don't need Enmity Combos] Enmity itself reworked to be based on elements of mob visibility such as positioning (visible, when contributing, to the mob directly, peripherally, or not at all; where WHM's Mist Cloak or Ninja's Smokescreen, by reducing visibility, then make the affected player's enmity even more "slippery") and "aura" (i.e. you, as a tank, are just really noticeable), whereby one can split their enmity output with stacked allies, mitigate said enmity by blindsiding, and tank-swap through well-timed positional replacement. Tanks' "tank stances" made far deeper and more utilitarian in nature, offering considerably more to depth of gameplay. All come to use the gauge in some way, and have neither global cooldown costs nor ability cooldowns longer than a GCD.
[What happens to enmity combos] Physical attacks now "stagger" enemy physical attacks, sapping their damage potential based on direct damage dealt/taken. Tanks' former "enmity" skills tend to lead in this regard, replacing the previous purpose with on-demand mitigation. Each point of Stagger taken increases a mob's Stagger Resistance stat, however, which then drains as the Stagger itself does. Thus, this works as a smoother form of CC. Attacks with little Stagger are best for setting up bursts of Stagger, while those with high Stagger are best for capitalizing thereupon and shutting down attacks. Note: Stagger applies as the animation begins (to hit the enemy), but does not begin to drain until the animation has finished (hitting the enemy); this makes skills like Butcher's Block and Rage of Halone particularly useful.
[What surrounds that] Virtually all attacks can be intercepted. This means that sometimes a tank's job isn't merely to stack up an arbitrary metric and meat-shield for others while aiming cleaves away, but rather to rush between mobs and their focused targets.
Gameplay-enabling abilities such as BotD, Enochian, and Gauss Barrel changed to traits. Many gameplay-centric traits moved up in level, to be built upon near to their former level of acquisition by further gameplay traits.
Certain abilities' cooling speeds now scale with one's GCD. This includes solely rotational skills or ones that would be disproportionately negatively affected (i.e. bottlenecked) by certain breakpoints in attack speed. For instance, Life Surge would now read "20 Turns", rather than "50 seconds". At a 2.40 GCD throughout the time it was cooling, it would therefore cool within 48 seconds. All animation times now also scale with GCD speed, to the nearest twentieth of a second. Note that all animations are currently rendered in 60 frames per second. [Until such time as animation breakpoints can be blended, a normally .8-second (50-frame) animation would then be reduced to .7 seconds (40 frames, frames 1, 6, 11, 16, 21, 26, 31, 36, 41, 46 redacted) if playing at a 2-second GCD, for instance.] Atop higher client-side trust when queuing actions, this should make double-weaving consistently possible and of far more consistent uptime cost whether playing at 30 ms or 200.