Powers & Abilities Actually, we already got a hint for Kiki Kyūtōryū Asura's new power up ...

First of all, there is one thing that should be known : what are Asuras (or Ashuras) ?
They are beings who follow the "Outer Path" which in Buddhism refers to any "wrong" method of pursuing nirvana, such as by asceticism (attempting to shed the physical form via bodily neglect, IE fasting to the point of starvation for example).
This is opposed to the "Inner Path" perceived as the right way to reach the nirvana by having mastery over the samsara and/or separation from it.

From the researches I made, I found that buddhist myths often describe Asura like mighty kings or devoted ascetics to the Devas.
Many mythical kings, who had started their reign wisely, wanted to undertake difficult “yogic” spiritual asceticisms out of devotion to the Devas. But the powers that these practices can engender push the aspirant towards pride and the misuse of these powers instead of guiding him towards detachment and "Liberation from human conditionings".
➡️ Justin Law, from Soul Eater, is a good illustration of this. Isolated with some trust issues, he constantly sought some form of guidance through the existence of an absolute entity to which he would be totally devoted. This extreme worship made him fall into madness and transformed him into a cynical, sadistic, violent henchman of Absolute Evil.
Usually, these kings, once they have become powerful thanks to the powers they have obtained, give in to their greed and perform, for long periods of time, more difficult asceticisms in order to increase their magical abilities.
They can then communicate with their chosen deity and obtain from this contact a power, for example that of not being able to be killed by another human. Protected against various dangers, they become demonic and abuse their position by terrorizing their subjects.
They sometimes go so far as invading the whole world, even the divine realms where they persecute the devas. Thus disrupting the "Dharma" (法 / "Buddhist law"), they therefore become the irreducible enemies of the Devas, powerhouses of spiritual progress and enlightenment, and shift out mortals from divine realization.
➡️ Typically what Asura, from Soul Eater, went through. As he got overwhelmed by his nonsensical fear of every thing (fearing death despite his status as an immortal Reaper, fearing his own weapon partner despite being far stronger than him, fearing anyone with unusual appearance), Asura developed an obsession with gaining the most power as possible to curb his fears. Falling into madness, his paranoia led him to eat and consume his partner in order to take away his powers and his soul consuming ability, which caused him to break the law of not hunting souls outside Shinigami's List. While he was supposed to maintain Absolute Order based on his sense of justice, he ended up becoming The Absolute Evil by plunging mortals worldwide into madness and chaos because of his senseless selfishness.

Now that I've set this up, I can explain my point : assuming that Zoro has developed his "Kiki Kyūtōryū Asura" technique through spiritual asceticisms, then if he undertakes even more difficult asceticisms, his Asura technique should gain a new ability.
But wouldn't that imply that Zoro, to perform such asceticism, had not only worshiped a chosen deity but that he will also manage to communicate and contact such an entity ? Which would be strange since Zoro said he doesn't pray to God.
But then again, does this really mean that he does not believe in an overwhelming existence whose will is the origin of every existing thing and the reason that everything continue to exist ? It could be that Zoro just decided not to pray to God because he probably said to himself that he must depend only on himself. His past as a solitary hunter goes in this direction but it is not a proof.

However, one thing for sure, Zoro often referred to Buddhist concepts in the names of his attacks (Urouge and Kaido have done it too) or in the sentences he recites to help him concentrate in order to perform a particularly complicated technique (Pound Ho).
This means that Zoro, through intense concentrations, taps into the Buddhist mythology to acquire new abilities (throwing flying attacks = Pound Hô, cutting everything = Santoryu Ôgi : Ichidai Sanzen Daisen Sekai, manifesting his mind in the form of an Asura = Kiki Kyūtōryū Asura).
These intense concentrations are perhaps the equivalent of Buddhist asceticisms and it will probably be through these kind of concentrations that his Asura technique will obtain a new ability : manipulating the shadows !
I think the fulfillment of Toki's prophecy will coincide with the moment where Zoro will be hit by the after-effects of the drug.
It will be a parallel to his duel against Kaido where he had to overcome his pain due to Hakai in order to inflict Kaido a fatal blow that was supposed to at least knock him down but ultimately failed. This time, since all the accumulated pain will be doubled, he will have to focus even harder to elaborate a technique powerful enough to take down Kaido once and for all.
This technique was prophesied by Toki, I may have the name of his new power : Rāhu.
In Hindu mythology, Rāhu is an Asura who has the particularity of being a shadow entity able to eclipse the Sun and who exerts an influence over a specific time of the day called Rāhu kāla (covering a span of 90 minutes each day, between sunrise and sunset, which can occur during one of the 8 parts of the day except the first part which corresponds to the dawn). This span of time is considered to be inauspicious.

Since the dawn is not under the influence of Rāhu in Hindu mythology, Zoro, instead of eclipsing the sun, will bend the 9 shadows of his swords, cast by the moon, in order to let known the brillance of the dawn through all of Wano Kuni.