I was working at my agency when the North Hollywood incident occurred. At the time my Midwest agency was around 1,150 sworn. We had just recently got our 4 round Remington 870's moved from a box in the trunk to an overhead rack in the front of the car. Loaded with OO Buck and a 5 rd box of slugs in the glove box. We had zero training with buck to slug transition. Shotgun training was just enough for the rank and file to pass the state mandated qualification with the shotgun.
The North Hollywood incident started "what if" type conversations with our command staff. Our firearms training staff looked into Ruger 9mm carbines (forget the model, the 9mm that looks like a 10/22). Keep in mind that we issued S&W 5906's, so there was no magazine compatibility from this PCC to our duty pistol. An AR patrol rifle was out of the question. Why you ask? Because AR's were reserved for new guy SWAT, as the rest of SWAT preferred the MP5's. And we couldn't have the rank and file Patrol Officer with SWAT type weapons.
It took a change in leadership of both the agency and of SWAT to see the value of the Patrol Rifle program. But not until 2005, and 50 initial rifles equated to 4 guns per shift per District that could be checked out by approved officers. The guns were carried in a soft case, unloaded in the trunk. In 2015 I took over a canine unit of 18 handlers. Shortly after taking over the unit, Dallas had an incident where 5 of their officers were killed by a suspect with a SKS. This motivated me to push hard, and I got my Canine officers issued rifles for their take home cars with the guns locked in rifle racks in front, just like the shotguns had been. Shortly after that, new patrol cars came with rifle/shotgun racks up front.
By the time I retired in 2021, every marked car had a rifle and a shotgun mounted in front. Why keep a shotgun? The answer was more simple than you might think. We already owned the shotguns and the trade in value for them was a joke.
Not every officer passed the patrol rifle qualification. Not all officers are "gun people". We all have some officers who only put in effort at the range because their state mandates they have to qualify if they want to keep their police powers. My state doesn't mandate patrol rifle qualification, but it does mandate pistol and shotgun qualification. So with a rifle and a shotgun both up front, the odds are that if you have a two officer car, both officers could access some form of long gun.
I have to wonder though, if my state were to mandate patrol rifle qualification in addition to shotgun and pistol qualification, would the complacent officers suddenly pay attention and put in the effort to qualify? One has to pass the state mandate qualifications to keep their police powers. And you can't work your favorite off-duty detail without police powers...
In my region, the Patrol Rifle program was actually a process that involved a cultural mindset change both within the agency and within the community. Both senior staff and the community needed time to get used to the idea of a non-SWAT uniform patrol officer with a rifle in their hand vs. a wood stocked shotgun. The mindset did change, but it took some time to do so.
I assume the Los Angeles area agency contemplating going to a 9mm AR already has 5.56mm AR's in the field? If so, then this change in cultural mindset would have already occurred. One question I would have is what is the motivation that is driving this change to a 9mm AR. I would hope that the motivation is not based on a woke agenda of preventing Law enforcement from possessing "Military Weapons" like a 5.56mm Military rifle.
I understand that LE is very regional when it comes to equipment, training, tactics and implementation thereof. If a 9mm PCC is the only option for your officer when the situation dictates they may benefit transitioning to a long gun, such as a motorcycle officer that needs to secure a weapon in the saddle bag, then I agree that a SBR type 9mm PCC with a folding stock might be the way to go. But I strongly disagree with the concept of forcing Patrol Officer's to trade a 5.56mm AR for a 9mm AR.
Are the suspects in your region trading their 5.56mm AR's and 7.62mm AK's in for 9m PCC's as well?