Back in chapter 406, when Aizen finished the Chrysalis stage of his transformation, he said this to Ichigo:
Credits to Cnet128 @ Mangahelpers for the translations I'm using
Aizen: ......You, I will leave in this place. // There is no need to consume you... // ...until everything has come to an end.
NOTE: I will NOT link manga sites, because I've been having a certain issue with them as of late.
Now that just seemed bizarre to anyone at that stage. Why would Aizen state he would "consume" Ichigo, a statement further elaborated on when Aizen said in chapter 419:
Aizen: Once, you destroyed the boundary between Shinigami and Hollow, becoming a transcendental being. // But now, you have lost the power you gained, and are but a shadow of your former self. // As you are now... // ...you are not even worth the trouble of absorbing and comprehending!
The intent behind Aizen's words were that he would "consume" and "comprehend" Ichigo's power. Most people probably dismissed this because they felt he was going mad with power. But here is what Yhwach recently said in chapter 620:
Juchabach: I will steal the Spirit King in his entirety. // As for Seireitei, I will cover it with a lid.
Juchabach: So that until I steal the Spirit King... // ...absorb him... / ...and consume him entirely... // None will be able... // ...to stand in my way.
In hindsight, it actually reveals what Aizen was planning to do: he was going to do to Ichigo the same thing that Yhwach did to the Soul King. When Aizen became a Transcendent, he didn't simply become "a being transcending Shinigami and Hollow", or even just a being whose power was so great that it could not be perceived by normal Shinigami and Humans; Aizen attained a power like that which Yhwach possessed, a Quincy ability.
I say it is a Quincy ability because Yhwach "consuming" the Soul King reminds me of Quilge's "Sklaverei" - Quilge used the reishi dominance of his Vollstandig to "enslave" the reishi of Ayon's body, absorb it, and add his own power to it. By comparison, Sklaverei is a watered-down version of Yhwach's power, which makes sense because I believe the Vollstandig in its entirety is the Quincy drawing out the latent power of the Schrift bestowed upon them by Yhwach.
But it is not simply Yhwach I am drawing a comparison to. Remember Aizen's teleportation technique in "Deicide":
Now, let us take a look at what Lille Barro did in the recent chapter:
Just as Aizen did in Deicide, Lille Barro was able to move from one location to another via teleportation. It is not just that, but people have also brought up a comparison between their respective appearances - an entity clad in white and possessing wings. In other words, when Aizen became a Transcendent Being, he developed abilities quite akin to the highest-level of Quincy ability.
It is not just Quincy ability, but Shinigami and Hollow as well.
As we saw in Deicide, and Aizen commented on, both Ichigo and Aizen's Zanpakuto melded with their right arms as a product of their respective evolution. Aizen hypothesized that this was the true form of the Zanpakuto/the proper form all Zanpakuto should take on (depending on translation), and I do believe that Aizen was correct, even if Ichigo's Zanpakuto evolution went one step even further. To this point, no other Shinigami outside of Isshin has displayed a Zanpakuto like that, or even the potential to reach such a level. Not even the head of Squad Zero had a Zanpakuto like that.
When Aizen reached his Final Evolution, the form looks so much like a Hollow because Aizen let himself be consumed by his negative emotions, the kind of emotions that cause Human souls to become Hollow in the first place. But even then, Aizen possessed the pinnacle of powers of a Hollow. He has no Mask, much like Ulquiorra's Segunda Etapa, and he gained the ability to use Fragor and Ultrafragor, the former being a small blast of reiryoku that did this:
As I stated in a theory thread on the "miracles" of the Hogyoku a long time ago, "the Hogyoku's power allows it to materialize events that would otherwise be impossible, so long as the "potential" exists for it to occur." As Aizen called the events brought about by the Hogyoku's power "miracles", that applies to himself as well in turn.
If I were to list the hierarchy of influences in Aizen's transformations, it would be like this:
His first form after the Chrysalis stage was predominantly Shinigami. The white robes created by the Hogyoku and his eyes indicate a Quincy and Hollow influence, but Aizen's power is still predominantly Shinigami at this point, as evidenced by only possessing the Zanpakuto melded with his right arm.
His second form was not only the point where Aizen said he had truly evolved into "a being surpassing both Shinigami and Hollow", but also the one where the Quincy influence upon his power is the strongest. He possesses wings in his form (the same number as Lille, in fact) and acquired the power of teleportation. His eyes are also now akin to how certain Quincy's eyes change when they enter Vollstandig, but the appearance of his wings more echoes Hollow influence, which is to be expected when the base for his transformation was Ichigo's reiatsu, specifically a Hollowfied Ichigo.
Nothing more needs to be said about his final form, where it can be said that his transformation into a Transcendent Hollow became complete. Just his physical appearance in this form is enough to tell you that much, and his two techniques used (and the high-speed regeneration immediately prior to the transformation) are both evidence of Hollow ability in this form.
When Aizen lost the power the Hogyoku gave him, it was not just the level of power, but the Quincy and Hollow abilities as well. Even then, Aizen still retained his power as a Shinigami, but at an even higher level than before (he didn't even need a Zanpakuto to mess with Yhwach's senses), and got even stronger while in Muken, to the point where his power in his normal form is intense enough to disintegrate a normal Shinigami's hands.
The concluding point of this entire discussion is that the nature of a Transcendent Being is not just one where, via a fusion of Shinigami and Quincy, and Human and Hollow souls, one can reach an entirely new plane of power beyond which any one individual of the four aforementioned races can reach, but it is also one that possesses all their abilities and the potential to wield them at their highest level.
Ichigo is the premier case of this phenomenon in Bleach, particularly now. Ichigo fights as a Shinigami using a Zanpakuto, but he also possesses the natural Quincy ability of the Blut, and the armor he's wearing right now is most definitely the influence of his Fullbring. If what Zangetsu did in Ichigo's fight with Zaraki is any indication, he may even be able to use the "Shadows", and I'm willing to bet that Ichigo is also a Quincy that can "share power with others", since that would tie into Urahara's explanation of how Inoue and Sado manifested power in the first place.
Even before the time-skip, we had Ichigo fighting with Hollowfication, and he is the only individual with the Hollowfication that we know of so far who could use both his Hollow Mask and his Bankai at the same time. People have complained about how Kensei and Rose did not use their Masks with the Bankai, but I think the reason is that they couldn't use their Mask and Bankai in tandem. A Bankai is the full manifestation of a Zanpakuto's power; a Visored Mask is the externalization of the user's heart, much like what a normal Hollow's Mask represents for them. Since the Visoreds are a hybrid of Shinigami and Hollow, I do not believe that they'd be able to use both Bankai and their Masks at the same time.
But the thing about Ichigo that does not make this immediately evident is lack of training. The times we did see him use Blut were completely instinctual, and Ichigo is more trained in the use of his Shinigami power than any other abilities. Hollow influence is still evident in his Zanpakuto (his Inner Hollow does double as his Shinigami power) as shown with the Black Getsuga in a recent chapter, but Ichigo has not trained his Hollow or Quincy abilities to be able to use Hollow and Quincy techniques, and his Fullbring, his "Human" power, is already fused with his Shinigami power.
On the other hand, the Hogyoku's influence made it so that Aizen did not need training to access these abilities, as they became natural and inherent with each transformation.
As a result, when there is another training arc in the future for Ichigo, I do hope that it will be one where Ichigo trains himself to be able to utilize all of his inherent abilities - not just Shinigami, but Quincy and Hollow as well. Ichigo has learnt about his roots and the true nature of his power in the past of this arc, but now he must train himself to effectively use all of his inherent abilities if he is to defeat Yhwach in the future, whom I firmly believe is the same kind of being (as is the Soul King), only he is a Quincy-dominant Transcendent.