Sounds overcomplicated to me, why would the average passenger care about half a million brands? I've suggested the brands "Express", "Metro" and "Network" before with the regions coming before e.g "East Coast Express" or "Network West Midlands". It gives a consistent overall brand for what type of service is operated while giving some distinction between the different organisations which run each region.
Because one benefit of the present system is that where multiple franchises serve a station you get the company name which can help differentiate services. E.g. London Midland service to Birmingham vs Avanti West Coast service to Birmingham.
If that just got replaced with the 12.37 Birmingham service is on platform 11. The 12.42 Birmingham service is on platform 18, you may lose that.
And if it works for franchises my thinking was make it work for groups of lines. Buses have numbers and often route names, LU has tube line names and is proposing to introduce line names to the Overground Network. Motorways have numbers.
But it wouldn't be the main branding, just a way to identify the service.
Would also help e.g. when it's announced on the radio "there are delays on the Brighton Main Line" or "the Central Transpennine line is currently closed due to an incident" just like when they say "on the tube Central line services have delays of up to 30 minutes".