Not sure what this guy, or other more idiotic open carry demonstrators, hope to accomplish. I imagine that, in states with open carry laws, there is public support for people carrying handguns openly in a holster. Probably much less so for some ninja'd out elite tactical operator carrying around his AR at low ready with 10 mags ready on his plate carrier.
This might not be illegal now, but keep this shit up and it will be soon. There is no reason to believe that a change in the law heavily prescribing open carry, if not outlawing it entirely, would be considered by SCOTUS to be a 2A infringement, especially if concealed carry is available as an alternative.
I'm always curious where the line between lawful open carry and unlawful brandishing lies in these kinds of situations. You often see pics of demonstrators in states that allow open carry where these goons have their rifles slung across the front of the body with a firing hand in the ready position. Seems that a creative prosecutor could decide to test the case.