Australia is pushing for client-side scanning too:
"We know there are a number of solutions that would ensure illegal activity online can be addressed, without weakening encryption and still allowing lawful access to information needed in serious criminal investigations. Solutions include: using certain types of encryption that allow proactive tools to function, implementing proactive detection tools at transmission, rather than on receipt, moving AI and proactive technical tools to the device level."[1]
The main problem with client-side scanning is that to have any effectiveness it requires a situation where "Trusted Computing" becomes a legal requirement for sale and use of computing or communications devices, where only registered operating systems can be installed and software can only be installed from registered application stores. And in terms of the Internet, registered operating systems would have to only permit access to registered web services, and registered web services would find themselves quickly unregistered if they allowed end users to execute their own scripts within a browser session. It'd require the end of "General Purpose Computing"[2] e.g. along the lines of regulations such as [3].
Criminals are being pushed increasingly down the Phantom Secure [4] path (developing their own technology that doesn't implement backdoors, client-side scanning, etc), and in response, public policy is increasingly seeking to outlaw[5] "General Purpose Computing" and the current decentralised model of communications. It'll take a long time, but perhaps over the course of the next 20 years we'll see the end of "General Purpose Computing"?
[1] https://www.esafety.gov.au/about-us/tech-trends-and-challeng...
[2] https://boingboing.net/2012/01/10/lockdown.html
[3] https://news.ycombinator.com/item?id=10139679
[4] https://en.wikipedia.org/wiki/Phantom_Secure
[5] https://www.esafety.gov.au/about-us/tech-trends-and-challeng...