Merseyrail and Transport for London services are both staying outside Great British Railways. And, of course, Transport for Wales, Scotrail and the Caledonian Sleeper are all devolved, so are also out of scope.
I don't think that is quite true.
The GBR umbrella will contain TfW and Scotrail, though continuing with local management and funding.
Merseyrail and TfL (notably LO and EL) have a GBR content, even if management and funding is devolved.
They all run over NR infrastructure, at least in part, and issue GB-wide tickets.
The GBR legislation will tell us what its limit of control is going to be in devolved areas.
I suspect the May branding will only apply to the GBR change process (currently GBRTT), with maybe a few token operational examples.
I think it will only apply to DFTO operations (the current 4 TOCs and any new ones transferring in).
Where Network Rail fits into this is a key issue - GBR is not just the passenger TOCs.