"More open communication between law enforcement and companies" as you said is the key, especially at the state and local level.
The thing is, at that point we'll have to concede that it's normal and proper for companies to be examining private communications. It's equivalent to a phone company keeping a log of all phone conversations transmitted on their network, then listening to them on a case-by-case basis. It strikes me as odd that it's illegal to do that for voice conversations but not illegal to do that for text conversations.
This is a Pandora's Box that I can pretty much guarantee Facebook does not want to open unless legislation is passed against their ever having civil or legal liability for doing so. Just speculate to the next school shooting where a parent/politician/newsperson asks "Why didn't Facebook tell us what was in their messages?"