With this rework idea, the stacks gained in Succession state are replaced with a Dimensional Energy Gauge; Succession Sage fills this new gauge with the Flow: portion of his kit.

Illusion Detonation: fills +5% Dimensional Energy

Finishing Touch: fills +15% Dimensional Energy

Form: Recall: fills +5% Dimensional Energy

Prime: Atomagia: fills +25% Dimensional Energy

When this gauge is at maximum, he can choose to retain the energy to gain a persistent +20% cast speed.

Alternatively, he can choose to spend his full reserve of Dimensional Energy to 'doublecast' one of his non-flow skills by imputting it a second time after the first:

Spatial Fissure

Ators Fist

Prime: Ators Mark

Illusion Compression

Prime: Spatial Collapse

Gravity Rift

Ators Energy

Void Gateways

Prime: Spear Bolt

Prime: Rift Storm

Prime: Rift Chain

Realm of Anguish

This plays upon his time manipulation theme in an organic way, and turns it into a key mechanic which encourages more aggressive play for decent reward.

The doublecast effect can interact with normal RC split/pocket function; so if you were to Ator’s Fist -> Prime: Rift Chain then attempt to use Ator’s Fist again, you'd spend your Dimensional Energy and successfully cast the 2nd Ator’s Fist.

To balance these doublecasts, the 2nd skill may need to be tuned down in some way, whilst still giving a player a reason to use them and spend their important cast speed bonus. (Done ideas could be increased range but reduced damage, an inability to CC or reduced accuracy. However, I don't know if this would be necessary, considering the cast speed and vulnerability associated with Succession Sage, in comparison to the high damage output and speed of other classes) 

In light of these changes:

Prime: Overdrive could double the amount of Dimensional Energy gained for the duration of the E-buff, which I personally feel would suit the skills 'vibe' very nicely.

Reset wouldn't really be necessary with this new mechanic, so instead it could be turned into a simple 'undo wounds' heal which restores 15% of max HP to self and allies, for a touch of utility in solo and group situations. 

Reasoning:

This doesn't overhaul his kit, but adds more depth to the kit he already has, with more rewarding skill interactions between flows and non flows, and more mind paid to what situations benefit from saving gauge or spending gauge, and which skills casted twice would be the most appropriate for a given scenario. 

Do you need to stay as fast as possible, or could you benefit more from twin Realms of Anguish?

Will an Ator’s Fist 'one-two combo' finish the fight or would you like to use two Rift Chains to get out of immediate danger? 

This was fun, hope you like the ideas and thanks for reading!