Just want to note that this effectively doesn’t apply to Verizon because they already have such a rule, which was imposed over a decade ago as a condition of the 700MHz spectrum.
This means we already know such a rule works for carriers and we can apply it to the others.
Actually, the original Band 13 700 megahertz agreement was that all Verizon phones would be unlocked from day zero. And they recently got a waiver from the FCC to increase it to 60 days. So, for Verizon, this would change nothing at all. For AT&T and T Mobile, though, this would be a major difference.