I think the tricky part has always been dynamic frequency selection, where the 5GHz WiFi radio is supposed to listen for a radar chirp and switch channels if it hears one. It's my impression that the hardware typically already supports some form of maximum transmit power configuration that the Linux drivers can further restrict but not loosen on the basis of the software's regulatory domain setting.

I have seen high-power WIFI card with amplifiers that can do really powerful TX output and the linux drivers are free to tune that output to its physical upper limit.

But this isn't about the case, you can always chain your router to an external amplifier (your SNR might be a bit flaky but that's another issue) you can always hard mod your router to do whatever you want.

This is a simple case of the routers adhering to the specs out of the box and that the spec could not be modified via software, and I really haven't seen that many TP Link routers that can actually broadcast outside of the "safe" spec, most of them can be unlocked to use the forbidden channels on 2.4 but their power limits are pretty low.

correct, even without amplifiers I have used high-power wifi-cards, however I have not tried any high TX output on any TP-Link products, which is odd why TP-Link becomes the target.

From reading the full document it seems that the default TP-Link software allowed the routers to operate at higher power levels.

"TP-Link violated the Equipment Authorization and Marketing Rules by marketing routers in the United States that were shipped with TP-Link software that permitted the user to change the country code for the router, thereby enabling the router to operate at a higher power than allowed on certain restricted Wi-Fi channels."

This doesn't seem to have much to do with OSS/3rd party firmware support which is a whole other can of worms that the FCC opened a few months ago. This is also seem to be limited to 5ghz only where I guess the US has more restrictions.

The bottom line of the settlement is:

1. You still can't load openwrt etc to TP-Link routers

2. TP-Link needs to do something (e.g. lock down their routers not to allow third party firmware like openwrt) to make sure nobody can increase Wifi output power above the permitted threshold

3. TP-Link have agreed to investigate ways of locking down their routers that don't block openwrt etc, but only so long as this doesn't force them to use chipsets capable of enforcing the restriction at the hardware level (because that would be expensive).