I think I recall emergency services switched nationwide in/by 2010, certainly it came to the small town (i.e. far from breaking new ground) I was in around then.
As I understood it at the time, it meant everything was encrypted and you could no longer listen in. But reading your comment and some of the details there (and having studied such things since then, albeit largely forgotten) I wonder if it's similar to your description, and it mostly prevented casual listening just because it raised the bar for the equipment needed, not because it was actually encrypted.
(Afaik before that it was analogue, or at least dual or slowly switching/some services analogue.)
Listening to the scanner isn't illegal here, so long as it isn't in the commission of a crime, but the ones that are encrypted obviously would be illegal to listen into without explicit authorization.
A lot of agencies want to keep their transmissions open, but with how easy it is to turn on encryption on their existing equipment, it only takes one incident for them to suddenly decide to encrypt.
It was disappointing when I moved from an area that had all but tactical channels in the clear, to one that encrypts everything. Apparently it even caused the state agencies to say they would not respond within the jurisdiction, for a period of time, as they were locked out of being able to talk to that jurisdiction's dispatch. Ultimately they were given encrypted access.
I wonder what percentage of people of working age have this privilege (or more precisely, have earned it!).
I'm very blessed to be able to tell people this. When I was growing up, my grandmother had a radio scanner in her small town Virginia home, and I was fascinated that you could listen in on what the police and fire departments were doing on a daily basis. My parents bought me a radio scanner a few years later and as a young boy I followed the rabbit hole of radio communications, scanners, and listening in to police, fire, aircraft, amateur radio etc.
Fast forward many years: I'm well established in a career as an IBM System Engineer, and during my downtime in the 90's, I thought it would be really neat if, instead of purchasing books with radio frequencies, it would be pretty cool if you could search on the WWW for this data. This was back in the day when this data was just starting to be made available on dial-up BBSs, but this new WWW thing was becoming more and more popular.
Mind you, I still pursued my hobby of radios and scanners, and had lots of expensive equipment to listen to everything around me. All the while taking multiple conference calls with IBM customers and generally doing my "day" job from home.
So, one week I sat down and taught myself Perl and MySQL. Created an online database, solicited people over Usenet to submit data to the new site, and RadioReference.com was born.
Fast forward to today. RadioReference.com is my avocation and vocation, I get to stay home and develop and manage my business which is also my hobby. And we did some amazing innovation which resulted in Broadcastify.com, which allows you to listen to police scanners all over the world without ever having to buy a complex radio.
So, yes, you can monetize your hobby, and this article really resonates. I never made it about the money, but my business is wildly successful and I can definitely tell you that I am living the dream :)