Wild Mass Guessing for Conversations with a Cryptid
Izuku does have a quirk but its a very subtle one.
Hisashi proves that one could have the extra toe joint and still have a Quirk. Considering All for One's brother /Izuku's biological uncle was believed to be Quirkless but had an extremely subtle Quirk.
- In a way, confirmed. Izuku was born with All For One.
All Might and/or Lemillion will be healed
As Izuku and All for One proved, Eri can restore people to their former states so they're good as they were before. Eri has all the reason to heal All Might considering how important he is to Izuku. Likewise, seeing how Mirio gave it his all to save her she'd probably want to help him out as well.- Confirmed. For both of them (Mirio thanks to All For One, All Might thanks to Eri).
Inko is related to Nana Shimura
All for One took an interest in Inko to begin with and her looks can't be the only reason. From what little we know about Inko is that she grew up in foster care and we don't know if Nana only had one child.- Confirmed.
Zach was a criminal himself
I mean, Zach's quirk is a Perception Filter that allows All for One to get away with his crimes and he runs the criminal forum board, the Conspiracy. He has had a much longer history, most likely cybercrimes considering his focus on the internet. Izuku is going to get arrested
When the government finds out that he published the expose, they will have Izuku arrested on censorship charges. Izuku will start working his way through stealing the quirks of everyone in the League of Villains...
...aside from Shigaraki and Kurogiri, who are either on the heroes' side or his side already. Given Dabi's very public attempt to kill Endeavor, it's highly likely that the remaining members of the League will take part in the riots against the government, resulting in Izuku confiscating their quirks. All For One's spy destroyed the Heroics Dorms with Hatsume's platform.
All of the students were sent home after the event, which was when Shigaraki and Kurogiri attempted to kidnap Izuku... but how would they have known Izuku would be at his house? Given that they were after him specifically, rather than taking Inko hostage, it's almost a certainty that the League's spy in UA destroyed the Heroics dorms specifically to ensure Shigaraki and Kurogiri had that chance. Izuku is recreating All For One's own origin story.
He has All For One (the quirk) and is using it to harvest massive numbers of quirks, even if it's to help protect people from rioters. He's also gaining extralegal allies via David Demir, his brother, and All For One's own contacts from Thailand. Meanwhile, a bunch of people are thinking ill of him for said collections of quirks, though they think he's All For One himself, rather than suspecting it's Izuku. Tomura might be filling in for the role of One For All - they're relatives, though cousins instead of brothers, with Tomura reflecting Izuku's turn to more villain-like solutions by going through a Hazy-Feel Turn into semi-heroism, and Tomura is already planning on trying to stop "All For One" from stealing the rioters' quirks.