I personally think, any speculations about a connection with PA cases are completely unsubstantiated. GB has been continuously trying to tell that child abuse cases are handled correctly, based on biblical principles. If AMIII really is facing any legal difficulties in PA, I am convinced that GB would stay together and fight. They would tell that such legal difficulties just prove that Satan is fighting against the org (similar as they have been doing with legal difficulties with shunning in Norway in the last months). Removing AMIII in connection with his handling of such cases would not strengthen, but weaken GB's standing inside the org.
And, given AMIII's age, his very straightforward and loyal talks, and the fact that in announcement he is explicitly called "brother", I don't see a chance that he is a kind of second Raymond Franz.
Theoretically possible are following scenarios:
1.) There was any wrongdoing requiring a JC. If so, I doubt that any future WT org's publications would enable us to draw conclusions on nature of wrongdoing (Elders schools highlightened importance of confidentiality of JC matters). I hate any speculations on kind of possible wrongdoing; especially in a forum dominated by ex-JWs it should be well-known that such speculations are often ill-founded.
2.) Recent new appointments changed majority in GB and made serious changes possible; AMIII is not agreeing with changes and decided to resign. If so, we should see any major doctrinal or organizational changes before end of 2023.
3.) He resigned for personal reasons, such as severe health problems, or severe situation in family. This would be very unusual for a GB member, but as AMIII talks were quite direct and straight forward, I consider it possible that he fells such an unusual decision. If so, they would not mention the reason in official announcement (as well as an announcement doesn't give reason if a congregational elder, or a regular pioneer, decides to resign for similar reasons). But I guess, that, in such a case, to avoid negative speculations, they would mention AMIII in an appreciative way, let's say, in a future monthly broadcasting.