To that point, they already do require that any firmware follow DFS and TPC when operating as an intentional radiator on 5ghz devices (and anything licensed for use in those bands without special licensing/regulation exemptions from them). The issue is, them requiring people do that isn't getting them to do it. Rather than run around slapping $10k fines (pulled from a dark area, no clue what the actual number is) on people who have openwrt running on 5ghz with the TX power set to 1000mw(actual value listed for the 802.11AC radio in my device in openwrt right now) with no DFS/TPC (DFS is not available in the wpad-mini daemon it uses by default), they're trying to make it so that people can't run openwrt. I can't speak to dd-wrt, but I'm guessing it's status is similar.
You can look at it 2 ways: 1, they don't want to potentially ruin a bunch of peoples lives or 2, they don't want to deal with it and are making it someone elses problem. Maybe it's #1 and #2 was the solution they came up with, I don't know, I wasn't on the committee that wrote it.
The unfortunate downside to this is, likely, this will also apply to any cell phone with 5ghz, any laptop/desktop with 5ghz, and a myriad of other devices. The barrier to entry to increasing the TX power on laptops is likely much MUCH lower than getting openwrt onto a router. I remember the old madwifi era windows driver for 802.11g atheros hardware you just had to go to device properties and set the max TX power to whatever you wanted. Later, you could just change that value from the default and edit a registry key.
My belief is the 'correct' answer is to require whatever part of the system handles this to be signed. This works well in cell phones already (the baseband/modem requires that certain parts of the 'radio' firmware partition (it's just a fast 16 image) be signed by the manufacturer or the radio won't turn on). Usually, the signed bit just contains calibration data for the particular RF circuitry, and if you tell it to operate on a band it's calibrated for, it just doesn't do anything. Applying this to routers will allow manufacturers the option of using cheap SOCs like they do now, and have to deal with signing the whole firmware, or have the option of using Fullmac hardware (like they pretty much have to anyways with 802.11ac) and then they can pass the 'signing and securing' buck to the RF manufacturers.
I'm wholly in support of their goal, but not their methodology. With the ever increasing amount of RF enabled devices, we're becoming more and more susceptible to bad neighbors ruining the party. The only upside to the potential to this being passed is, any of your neighbors who are operating their hardware outside it's rated spec will have a hard time when the device eventually cooks itself(if you look at 'high power' 250/500mw wifi cards, they all have great big heat shields on them that get burn you hot when they're operating at high power. The little SOC chip doesn't have that, so running it out of spec shortens it's life).