Unsure about the planned ETCS policy. Certainly none built at present. I'll find better sources for what is present and make some changes myself. I have contacts working in the Reading signalling design office.

ETCS L2 is not yet commissioned for use outside of the Heathrow Airport tunnels, nor is it planned for installation beyond Reading.

The route as a whole is Great Western Main Line. The two pairs of lines are known in turn as the Main Lines and Relief Lines (instead of the usual Fast and Slow). Indeed, the Great Western Main Line also carries freight and other services, but it was named after the original company that built the line, and not the present company that operates some of the trains over it.

Renaming the entirety of relief lines along the Great Western Main Line to "Elizabeth Line" is not correct, the infrastructure name has not changed, and mixed services both Elizabeth Line, GWR local services and freight services still use them.