As Scotland and wales have their own branding and liveries, the neatest solution would be to roll-out the Greater Anglia livery with the double-arrow across the Network. It features England's colours without being overtly nationalistic and has shown that it's adaptable, working on several types of rolling stock and on inter-city, regional and local services very successfully.
Greater Anglia also has great punctuality and cancellation rates, so it's a good contender for creating an "improved" look.
I wouldn't expect there to not be too much "rebranding" taking over the entire network and changing EVERYTHING would cost an absolute fortune not to mention a long time. I'm sure we will see a centralised training center and a GBR management "team" plonked on top of all the TOCs
A total rebrand and total "takeover" would cost so much, in fact I expect the government couldn't afford to take it all on. I mean just taking over the lease of every train in the country.... you imagine the cost.... and they want to keep ticket fares down.... if they do that tickets will go up to fund it no?
Taking over the TOCs would also bring in whatever money they were getting with their contract to operate the service. It may even be ideal to get rid of the ROSCOs over time as it would be cheaper (long-term) for the
government to own the rolling stock. If management is merged then half of it could be cut out to save costs as I'm sure there is a
lot of unnecessary overlap in areas with multiple TOCs.
I think at ground employee level we will hardly notice a change.
I think operation-wise it'll be nearly identical, but I am curious to how staff leisure travel will work afterwards. There's a lot of weird acceptance between seemingly unrelated companies (Merseyrail accept GA staff because they're both owned by Transport UK Group), though every member of gateline staff that I've met has just allowed anybody with staff travel cards through any barriers (Northern staff through GA barriers, for example).