Not to put too fine a point on it, Sony's security practices were so negligent, anyone could have done it. The tools used were very unimpressive and easily available.
The evidence linking this to any nation-state at all at the moment is incredibly weak, bordering on non-existent.
Not just "anyone", but there could've been multiple unrelated groups hacking them at once. Didn't they say there's some evidence of hacking from 2 years ago? Some of them could've just hacked them and Sony never found out about it.
The evidence linking this to any nation-state at all at the moment is incredibly weak, bordering on non-existent.