It may be simple to avoid, I myself don't have to worry about this as much as I'm on a byod sim prepaid plan, I can just buy an unlocked device, but the truth is that many phones on ebay are used phones, many of which were carrier subsidized. and used carrier phones are normally cheaper than the full unlocked versions. This move could kill a substantial part of the second hand market.
This is about greed, carriers can make it harder to switch by refusing to unlock your phone, even if your contract is up or you've left and paid the etf, which in reality pays for the rest of your subsidized phone not the mention the boom for phone manufacturers to increase sales, as more phones become harder to resell.
With T-mobile's refarm and bring your own device promotion. I fully expect AT&T to start refusing to unlock phones, regardless of your contract being over. Verizon and Sprint may be better about it, as their phones aren't easily moved from one carrier to another. It's anticompetitive and anticonsumer, they shouldn't have the right to tell you what you can do with a device you own.
It seems that way after reading the pdf. They are trying to stop a practice of a company buying used phones which are out of contract and therefore can be unlocked and are later sold in other countries for full price.
Therefore they are now not required (by my understanding) to unlock that phone even after contract is up.
So in short consumers should now buy unlocked and not subsidized phones. If carriers don't want to activate your unlocked device because their firmware is not on the phone then they could also tell you to go screw yourself.
Which damages the used cellphone market and will also give carriers greater control of what devices are on the network and how they are used.
In the process though it gives us less options so they can feel safer. It's also a indirect benefit for handset makers and allows for the use of backdoors because it's "Their firmware".