Much of the 5G progress happens in the core network and network interconnects.

As far as I remember, there will be some sort of "layered" encryption. The innermost layer is the user's payload, end-to-end encrypted between operators. Each service provider (responsible for transporting the data) adds patches with modifications and a signature by the service provider.

Not sure if that actually made it into the standard yet. I think the motivation is that roaming requires cost-effective routing, fraud detection,.. so there's a whole business ecosystem around that.

Long story short: I think people are working on this