Threatening to intentionally bean a guy is threatening to assault him under the guise of fair play. It should absolutely be a suspendable offense.
You see how we're all trying to psychoanalyze Sanchez to decide if his HBP was intentional? A guy publically stating his intent on social media is *telling us what we're trying to speculate*. If a guy is just going to out his intent, you get him for it. It's hard enough to stop headhunters, so you nab the idiots who advertise it.
I'd even go so far as to say that the player in question should be prohibited from pitching in any game in which he will be facing the other guy's team.