To answer seriously: unfortunately, the UK is one step ahead with the Online Safety Act. They’ve already given Ofcom the power to enforce client-side scanning. Ofcom themselves are deciding whether they want to use this power yet and this should happen sometime next year.
Just as a warning, this is licensed under the AGPL, with a CLA that requires copyright assignment. So, they could pull the rug at any time:
2.3 Outbound License. Based on the grant of rights in Sections 2.1 and 2.2, if We include Your Contribution in a Material, We may license the Contribution under any license, including copyleft, permissive, commercial, or proprietary licenses.
It’s not perfect yet, but it’s much, much better than the old days.
OMEMO is supported by every major client, and they interoperate successfully. Unfortunately, most clients are stuck with an older version of the OMEMO spec. It’s not ideal, but it doesn’t cause any practical issue, unless you use Kaidan or UWPX, which only support the latest version.
All popular clients and servers support retrieving chat history now too.
In practice, I’ve been using it for several months to chat with friends and family, and haven’t had any issues.
I think (and hope!) it would likely only get applied to the biggest services, and would be enforced by removal from the app stores.
Then, the logical next step for the government when this doesn’t work would be to allow this requirement at the OS level.