It appears that this has been added to the post-landing taxi script, as an announcement was made today on 316 (welcome to YUL, local time, etc, social distancing while deplaning, yadda yadda).

It didn't look like there was a ton of effort made by the passengers, but the utility of the policy seems questionable, given all these people have just spent hours in proximity to each other, and there's really no way to do it anyway.

But the policy was definitely clearly announced.