Robert Maxwell wrote:
As far as I can see the only flaw in the confession is the money Walt payed for medical treatment. Why would a drug kingpin need his employee brother in law to pay a couple hundred thousand in medical fees?
Deniability. Think about it. DEA agent on a modest salary is paying for almost $200K in top-notch rehab? I don't think so. Instead, use a cover story that your gambling addict brother-in-law paid for it with his winnings, instead. The best part of said cover story is that it's (mostly) true! This puts all the risk on Walt, which fits perfectly with the narrative of Hank blackmailing and threatening him into doing it. The whole thing hinges on Hank being this master manipulator, a more shrewd kingpin than even Gus Fring. His relentless pursuit of Fring, by the way, is cast in an entirely different light once you believe he was using DEA resources to thwart his competitors. This might be a smarter move by Walt than we realize, though it has no evidence to back it up other than the money Walt paid for Hank's treatment--which is, as Hank said, the "nail in the coffin" for him.
So Hank became a drug kingpin, committed murders, etc for $200,000? Where's the rest of the money? Right now, Hank really has no motive for being Heisnberg unless someone could find millions of dollars hidden away somewhere (I'm tempted to do one of those lame ass "oh wait" takes here).
This is the reason, I think, Hank initially referred to Walt's confession as a threat. There is no evidence other than Walt's word that Hank is Heisenberg.
I took the 'nail in the coffin' remark to be a reference to Hank's career if the video were given to the DEA. Because it would be highly unlikely that Walt's 'confession' alone would be enough to even get a case to trial against Hank, despite the $177,000 rehab payment. But the video would certainly place Hank in a position where his personal integrity could become an issue and that alone would probably end his government law enforvment career.