Someone starts shooting #2 or even #4 TSS, and that could certainly create some safety issues, as well as some ethical issues with hunters attempting to body shoot birds at long ranges.
I know the Dead Coyote Hevi-Shot will roll coyotes at 60 yards with the right gun (I believe #T in Hevi-Shot).
At some point if issues arise we could see regulation in shot size and/or density. Not sure we need anything more dense than say 15 g/cm³, but that is another topic and thread.