Everyone else seems to be going all out
Ashura is coming back,when ? Who knows.
Oda doesn't forget attacks like that.
Why hasn't it come back ? It's a mystery but i wouldn't look too much into it as sometimes Oda makes questionable choices without much thought nor reasons behind them.
When Zoro uses Ashura,it is bound to be more impressive than anything Zoro has shown so far though.
Asura isnt coming back just like Zoro isnt fighting Kaido.
I already said this in another thread, but my prediction is:
1. All the remaining match-ups in Onigashima are getting finalized soon. All the remaining SHs, PNM alliance, Calamity, and F6. Maybe even WB remnants and BMP.
2. Act 3 ends with Hybrid Kaido taking down the SNs to finish off the Act with a tragedy.
HOWEVER
Act 4 Main Fight resumes with Zoro channeling Ashura to fight Kaido while Luffy and the other SNs are out.
If we take Shonen tropes into account, then obviously Ashura Zoro won't finish off Hybrid Kaido solo because of these possible reasons:
1. Big Mom's intervention.
2. King's intervention.
3. Hybrid Kaido has an even more insane regeneration/healing factor.
4. If Ashura is a form, it likely has similar drawbacks to G4.
5. If Ashura is an attack, it likely puts a strain on Zoro (like Amakakeru Ryu no Hirameki did on Kenshin).
6. Combination of 4 & 5.
However it plays, Ashura Zoro eventually fails to stop Hybrid Kaido permanently. Kinda like 8 Gates Guy vs Madara, for reference.
Then, once Zoro has to stop channeling Ashura, Luffy bails him out (like how Zoro has bailed out Luffy 4 times in the whole raid, so I guess Oda will make Luffy repay the favor at least once).
The story then continues with Luffy trying to get the job done as Zoro recovers so he can rejoin the fight later to finish off Kaido for good.