That was my first thought (Birmingham to Brighton had some merit but not the northern section). The Newcastle bit felt like a token side-salad, only included to generate a bit of publicity in the North East (headlines in the local press there like "Sunderland train operator seeks new Gatwick link", that kind of thing)
But, London to Newcastle seems a lucrative market.
If you were an OAO with several services a day from London to Doncaster (the Bradford service, maybe one day a Cleethorpes service), and from London to York (the Sunderland service), maybe there would be potential for GC- specific tickets from Tyne to Thames (changing in Yorkshire), maybe even some demand for GC-specific Sunderland/Bradford to Birmingham etc tickets
Pure speculation, of course, but (AFAICS) this would be the first chance for an OAO to offer through tickets between their services
(that's assuming that it has any likelihood of happening whatsoever, and that anyone would risk connections between long distance services when one of the trains involved is an unreliable 180)