No one will be locked into stock firmware if the router is in compliance. It's what's Asus is doing now in the US but didn't think much of a better solutions for others.
Bu if you have 3rd parties that do not live in the USA making firmware out of spec for the USA and people who live in the USA are installing said firmware...manufacturers may end up having to go completely closed source.
Openwrt, Tomatousb, DD-WRT, Merlin would no longer have a source for any future firmware builds which would put an end to anyone using non stock/3rd party firmware.
Unless they could figure out how to decrypt the firmware.