Ticketing and stations will be GBR-branded, but I'm not sure about trains, certainly in the 2-year transition period.
First Group have already been given a 2-year contract for SWR and TPE, and GWR has just been extended.
GBR will have 5 Regions, presumably mapped on to Network Rail's new Regions:
Our [NR] five regions are Eastern, North West & Central, Scotland’s Railway, Southern and Wales & Western.
This may mean current TOC areas may be merged (or maybe not).
What happens to Thameslink and XC region-wise?
While GBR may be added to liveries, I doubt there will be a major repainting exercise until the new TOCs start up.
Long distance may be different anyway, and more like today.
I also can't work out if the GBR double arrow will be the same as the old one, it might have some subtle "development".
Looks like Scotland and Wales can have their own branding locally, but will need to cooperate with GBR standards.
New "best in class" retail web site too.