Actually, this bill just changes the existing warrant requirement to apply to a communication stored more than 180 days (the warrant requirement already exists.)
The argument is that one aspect of the existing warrant requirement is that it burdens the defense in certain circumstances (I don't think anyone would argue that the arrangement in general -- or this bill's changes -- simply favors the prosecution; without the warrant requirement, while the defense might have more access to certain evidence once a trial started, police and prosecutors would have -- and do have, now, for communications outside the time limit of the existing rule -- more ability to conduct arbitrary fishing expeditions without probable cause before a trial started.)
I would think those whose concern is primarily with the rights of the criminally accused would like the warrant requirement for police investigations but would want some provision for criminal defendants to get access to communications that might be exculpatory evidence, even if it has similar requirements (probable cause showing) to a warrant that would be sought by police/prosecutors.
Before 180 days, you need a warrant. After 180 days, you need a (d) order. Can the defense can get it using a 18 U.S. Code § 2703(d) order? In my view, the answer is no. The statute specifically refers to a "governmental entity" being able to seek the order. I don't believe that includes criminal defendants.
See: https://www.law.cornell.edu/uscode/text/18/2703
"A court order for disclosure under subsection (b) or (c) may be issued by any court that is a court of competent jurisdiction and shall issue only if the governmental entity offers specific and articulable facts showing that there are reasonable grounds to believe that the contents of a wire or electronic communication, or the records or other information sought, are relevant and material to an ongoing criminal investigation."
What if your hypothetical Facebook video was < 180 days old?