The way I understood it is it being a system that will let you choose rather flexibly how you want actions to be represented that are directly chained to each other.

Using Dragoon as an example, Jump/High Jump is the only way to access Mirage Dive, so you can use this system to make High Jump turn into Mirage Dive when under "Mirage Dive ready) or you can keep the hotkeys separate, depending on your preference. Same will likely apply to the combo paths for Heaven's Thrust, Chaotic Spring and Coerthan Torment.

So putting aside regular combo actions, this will give you flexibility for the following actions:
  • PLD - possibly Requiescat -> Confiteor -> Blade combo + Atonement combo, Fight or Flight -> Goring Blade
  • WAR - possibly Inner Release -> Primal Rend -> new finisher OR Inner Release into new action for using 3x beast action under IR
  • DRK - Living Shadow new continuing action
  • GNB - new Bloodfest combo, No Mercy -> Sonic Break
  • SAM - Ikishoten (+50 gauge) -> Ogi Namikiri -> Kaeshi: Namikiri, Meikyo Shisui -> Tsubame Gaeshi
  • RPR - Arcane Circle -> Plentiful Harvest, Enshroud -> Communio
  • MNK - new Riddle bonus actions each, rest unsure
  • NIN - Bunshin -> Phantom Kamaitachi
  • BRD - Wanderer's Minuet -> Pitch Perfect, Apex Arrow -> Blast Arrow, Radiant Finale -> new finisher
  • MCH - either Turret/Queen -> Overdrive or Automaton Queen -> new missile barrage finisher, reassambled: Chainsaw -> Chainsaw 2 (possibly other powertools as well), Hypercharge -> Heat Blast/Auto Crossbow
  • DNC - Devilment -> Starfall Dance, Fan Dance I/II -> FD III, Flourish -> FD IV or new Flourish bonus action, Saber Dance -> Saber Dance 2
  • BLM - Ley Lines -> Moving Leylines or Between the Lines, Fire IV <-> Blizzard IV, Flare <-> Freeze, Despair <-> Umbral Soul (all depending on current aspect)
  • SMN - Summon Bahamut/Phoenix/Solar Bahamut -> their respective Enkindle, Searing Light -> new combo action
  • RDM - melee combo, aoe combo
  • WHM - Presence of Mind -> new PoM attack action
  • SCH - Chain Stratagem -> new CS attack action
  • AST - Divination -> new Div. attack action(?)

This list is SPECULATIVE and not indicative of the final product but what can be expected.