It's highly imprecise, but not impossible. The alerts are already "this is over some threshold of ground acceleration", so there's an inherent severity estimat

It's highly imprecise, but not impossible. The alerts are already "this is over some threshold of ground acceleration", so there's an inherent severity estimate in the alert going out at all. But expected intensity information isn't included because: 1) it's still a very imprecise estimate at that time, 2) actual intensity of ground motion (what you care about) will vary dramatically by location, and 3) people don't deal well with that kind of information in an alert that is really meant to be "hey, take cover".