The whole process, although annoying, was painless. The tech gave me the option of them trying to fix it by blowing dust out or just replacing the entire keyboard. I elected for the later given that it's a design fault. The repair took 1 1/2 days which I had done when I was out of town.
Since they glue everything together, getting a new J key also meant a new keyboard, touch bar, finger print reader, speakers, battery and touch pad. Which if there was no recall I can imagine would be a costly exercise. Hopefully after the recent recalls Apple engineers will be looking at making easier to service components.