1. The new cameras followed the trend of PCs. As faster processors and more RAM and larger HD became rapidly available, your PC was obsolete the moment it was purchased. New model, after new model, after new model waited in the wings? And now it's all leveled off. No talk of "processor speeds", what have you.
2. This was true with cameras and "megapixels". Mine (Nikon) has 24. It was made in 2012. Their latest Z (2019) also has 24 MP. I'm good. This is leveling off like PCs did. And that's why I disagree with those who kvetch about the product lifecycle of digital cameras. It was following the doubling of MP resolution as the PC market did with processor speed, RAM, and storage.
3. It will be interesting to see if Sony stays in the market after two years. I know, I know -- they're all the rage at the moment. But Sony is known for going in and out of consumer markets -- consumer audio, HDTVs, smart phones... and the other electronic giants Samsung, Casio bid hasty exits from the consumer photographic segment. Much of Sony's success will depend on their penetration into the professional market as opposed to advanced amateur segment.
This is one of the reasons why I stick with Nikon and if not Nikon, Canon. Nikon over Canon because of decades of backwards compatibility resulting in mass-produced high quality used glass that's reasonably priced, and great sensors. Nikon right now provides the best bang for the buck -- hands down. (Canon is falling behind in this [sensor tech] area. Leica is a joke. Sorry. They just are.) Plus, I feel a certain loyality to the companies that have served the photographic community for over 100 years. And I simply don't trust that Sony will be around in the long run -- especially if a market is poised to rapidly shrink by 50% in 24 months.