There is more momentum toward these inner composite + koto with larger headsizes 159mm+
With the bigger headsize you get the flex of those inner + limba while having the crispness of koto for close to the table backhand exchanges.
H301/N301 was probably the first successful implementation then followed by Cybershape Carbon and now AcB.
As boosters become more potent, users of outer-type Vis blades may appreciate the added control and stability provided by an extra intermediary wood layer, while inner-type W968 players who already soften their sponge through boosting now have the option to transition to a harder wood for increased power and precision.
Also, I suspect the delay may be due to waiting for improved manufacturing and wood drying techniques to help keep the weight down, especially since koto is a harder and heavier wood compared to limba.
The first batches of H301 I saw were mid 90g+ along with the thin handle they felt extremely head heavy, I hope the weight and balance AcB is much better now.