I think the key to this "mystery" is Affleck. HE'S clearly not up to his tits in a drug-addled haze, and he seems to be enjoying himself a little too much to be filming his friend (and family member) going down a very dark path.
Joaquin is way, way too incoherent, dirty, and "obviously" fucked up for this to be anything more than an elaborate prank. Seriously, I don't buy that his little fall off the stage after that embarrassing mess of a performance was anything other than planned.
Of course, I could be wrong, but I don't think I am.
If Affleck wasn't trailing him around filming all this mess, I might be less skeptical. But he seems to be going too far, too soon; he's tipping his hand. That fucking beanie? Please. That's a little broad.