IMHO, a NDA should always be limited in time. I am pretty sure twillio would not request a judicial review for a NDA lasting a couple of weeks. For a NDA lasting more than a year, a judicial review seems justified. Avoidind judicial review may be a good motivation for FBI to use shorter NDA. This would benefit to transparency.
The "A" in NDA stands for "agreement", but NSLs are not jointly agreed upon: they are the one-sided assertion of the government's authority.
Not disagreeing with the idea that there aren't a variety of reforms that seem mutually beneficial, such as shorter timeframes — just noting that there are not equivalent to NDAs.