I'm not familiar with US legislation, but from my perspective this is just Musk on his soap-box making a statement. It's not something I can rely on while building a business that possibly (!) infringes one of Tesla's patents. They may retract their statement and reconsider at any time, especially when times get tough.
It's nice to hear this, sure, but I fail to see the meat in this announcement.
Beyond that, anyone who wants something signed and in writing could likely drop a note to Tesla for it when doing their due diligence.