After receiving the original version of the All For One quirk, Tomura Shigaraki is in a state of conflict. He can hear his master’s voice trying to control him, but he has been able to maintain some measure of control. However, I don’t think Shigaraki will maintain control for long. This is probably due to the fact that All For One himself is still alive.
Just as Izuku Midoriya has a connection with the previous wielders of One For All, Shigaraki clearly has a similar connection with his master. While the One For All vestiges guide Izuku, All For One is clearly trying to control Shigaraki and take over his body. Because he is in a state of mental and spiritual conflict because of his bond with All For One, Shigaraki cannot exert the full potential of his new strength. I think in order to make All For One’s voice stop and assert complete control over the All For One quirk, Shigaraki will have to kill his master.
Killing All For One would be Shigaraki’s final test and the only way to truly consolidate his new position as the new king of the underworld. The world is not big enough for the both of them. In Star Wars, the Sith would betray and kill each other and this tradition was most prominent between masters and apprentices. A prime example would be Darth Bane’s Rule of Two, which dictates that there can only be two Sith at any given time, a master and an apprentice. When the master becomes weak, the apprentice overthrows the master in order to become the new Dark Lord of the Sith. My Hero Academia creator, Horikoshi, is a devout fan of Star Wars and has included several references to the Star Wars franchise in My Hero Academia.
All For One has clearly become weaker than he has ever been. Not only was he crippled by All Might, but he has been imprisoned. While being imprisoned, All For One is completely restrained and has guns on him at all times. He is blind and cannot even breathe on his own anymore. All this time, we thought All For One was grooming Shigaraki to be his eventual successor. However, it looks like All For One has been preparing Shigaraki to become a stronger and fitter body for his essence to inhabit. This is similar to what Darth Sidious tried to achieve in Rise of Skywalker.
My guess is that All For One is currently in the process of trying to transfer his essence into Shigaraki, but Shigaraki is maintaining some semblance of control for the moment. My Hero Academia fans have speculated on a prison break story arc in the near future. Due to this, I think Shigaraki will try to break into Tartarus Prison to not only kill his master, but also free every supervillain inside to increase his army further. Once All For One dies, his attempt to take over Shigaraki’s body will be severed and the all For One quirk will truly belong to Shigaraki.
I believe that the progression process of the Shigaraki’s surgery was to prepare him for All For One to take over. When the superheroes disrupted the process, they made All For One’s attempts to take over Shigaraki imperfect and incomplete. That is why Shigaraki is able to maintain some measure of control. The superheroes believe that they were trying to stop Shigaraki from powering up, but they may have unwittingly helped him. By disrupting Shigaraki when he was 75% complete, the superheroes may have interfered with All For One’s plans to take over Shigaraki. That has a sense of irony because the superheroes tried to stop Shigaraki but they inadvertently saved him. With his surgery incomplete, Shigaraki has a chance to fight All For One’s control long enough to sever it during the prison break. When that connection is destroyed, Shigaraki will become All For One’s successor for real. We shall wait and see.