"Fair Use" relates to copyright and the use or reproduction of copyrighted material for specific uses. It is not related to the ability to use a device.
In my very amateur interpretation, in the past the DMCA has been used as a basis to prohibit access to a phone's software and firmware, the argument being that the protection schemes are in place to protect rights in the software and firmware. All this rulemaking is apparently doing is saying that for the specific situations noted, copyright protection is no longer an accepted basis for limiting access to the software or firmware. It is not saying that manufacturers cannot put such protection in place or that there may not be another basis for prohibiting access and it is not saying that phones have to be offered open. In addition, distributing to the public technology, products or services intended primarily to circumvent software or firmware protection is still prohibited by the DMCA.
Based on that, the one line item seems more aimed at allowing developers access to a device's software and firmware in order to insure compatibility with apps, provided they are legally developed and obtained. It actually seems to support the carrier and device neutral Android app approach over the Apple approach.
The other line item almost seems to be aimed at allowing used phones to be activated on a different carriers. The limitation to used phones seems to not actually prohibit any new phones being locked down and I see this being intended to allow someone that has fulfilled their obligation to the original carrier to take their phone to another carrier. It seems limited in doing anything much more than that.
From other interpretations I have read, this does not make rooting "legal" or prohibit manufacturers limiting access to any software or firmware as much as it prevents DMCA being used as a basis for suing someone who does circumvent that access control under the conditions listed, such as to load a legally obtained, third party app or to activate a used phone on a different carrier.
Like I said, just one very amateur personal interpretation by someone not an attorney, but I think that many people are reading more into this than there really is.