Even if people are registered, sometimes in the circumstances it can be very difficult to contact them. If you're dealing with a hurricane or an earthquake, it can still be difficult to contact them.
That's something that Global Affairs would have to tell you: what types of things might be possible, what sources they could use to collect that type of information, and what type of effort would be needed to collect it. It's always difficult to tell people they have to register and to make them actually register. It would be more a matter of whether there are sources of information already collected that Global Affairs could somehow tap into that would help them understand who is travelling.
I don't really know how feasible this is. It's something the department would have to explore.