No, it's been in place all along. It is up to the specific carrier to decide whether or not to enforce this or not.
Kind of the same thing where on UX, you are sometimes asked to put your window shades up for T/O and landing, but on mainline, it's never mentioned.
As a rule, your average UX f/a has been on the job for a matter of months, if not weeks. They are fresh out of their training where they had this crap drilled into their heads for 6 weeks, and are told that anyone could be an FAA inspector looking to levy that $1,000 fine on them.
Actually, FAA inspectors are required to identify themselves prior to boarding, flying and inspecting your flight.
Even though we want to think these individuals are on 'power trips', in actuality, they just had really good brain washings in their trainings weeks earlier...nothing else. They are just afraid for their jobs. If you can call it a job. (and yes, I am aware that I once walked among them and did the same sort of crap! )