I lanesplit 30km each way every day on a very congested highway. Highway is safer than backroads, where people haven't woken up yet, and are all ty to take every gap they see.
Highway is at least a fairly stable level of dangerous. But on my route i know about 10 regulars, and hundreds more that you only see once.
I've picked up some guys off the tar, but most of them were noobs, who were riding in the wrong place, and too fast. We ride similar speeds, and a few of us are the "thankers" ... trust me a small wave when a cage pulls over for you goes a LONG way!
I'd split even if they made it illegal. No ways a cop will keep up in traffic with his panniers etc.