It's pretty clear that neither pilot saw the other, and whilst looking at a shaky video is always subject to interpretation, my sense is that on those trajectories, there's a pretty good chance that neither could have seen each other.
If that's the case then there's really only one solution - to make the corridor controlled airspace, still accessible by GA, but subject to proper control. No-one likes to see that, but unless you're prepared to see one of these 'flukes' every few years, then that's the only way out.
Imagine if the London or Paris heliroutes were a free for all, of course sooner or later something like this would happen.