The article I read was quoting some larger data set and didn't go into details.
The cell phones are taking the place of the small low end point and shots. Some of the high end cell phones are probably cutting into mid range, esp fixed lens cameras with people who just want a picture - no need or desire for high IQ images. A certain % of those people will start to get the bug for more versatility and higher IQ images and move up to good quality fixed lens, mirrorless and dslr interchangeable lens cameras etc. And of course there will always be a % who want high IQ and versatility from the beginning. As to upgrades, the tech keeps changing, often in big improvements but when the improvements get to be small increments, like with most computer gear, people will start to stick with the gear they have for a long time, not seeing any need to upgrade as long as their gear works and gives them acceptable IQ.
A mature market, then the camera companies will have to go through a major adjustment in the way they do business, how many models they offer etc. If anyone comes out with an affordable camera body that can have parts upgraded like tower computers then a larger % of people will go for that (I assume high end) body and upgrade instead of getting a whole new camera. Esp if it is in the realm of newer sensors and controlling software. In the film days the cameras pretty much kept working for many years and you added newer lenses while just starting to use the new improved films in the same camera for many years. My Miranda Sensorex was purchased in late 67 or early 68 on R&R in Tokyo (I forget which) and I continued using it, plus a second body obtained in the early 70s and an Olympus body adapted to use on a telescope until I went digital around 2000, they are stored and still work if I ever get the bug to try film again.

You’re all a bunch of wankers. It NEVER made sense to be that the lyric was changed for the live concert (in Central Park). The song is Kodachrome for gawd sakes. Colour! Of course everything looks worse in black and white. My first SLR was a Pentax (1976) but my second was a Nikon and all my DSLRs have been Nikons. I have been a Paul Simon fan since he and Art were known as “Tom & Jerry” and cried when they split in 1964 after “Wednesday Morning, 3 A.M.” sold poorly. I loved the “Paul Simon Songbook” recorded solo in London in 1965 and rejoiced when they re-grouped and gained success as Simon & Garfunkel through the late 1960’s. If you want to have some fun, listen to “Wednesday Morning, 3 A.M.” and then “Somewhere They Can’t Find Me” recorded in 1966 and released on the “Sounds of Silence” LP.