"InterCity" doesn't really exist. It's archaic to how the railways have evolved:
- Project 110 enables 350s via the Trent Valley to hit MKC and Rugby quicker than the 80s used to!
- OA has led to "non-BR" operators like Grand Central
- The Cambridge Cruiser isn't that different to Gatwick Express - which was once "IC".
- Norwich is now run by EMUs. Corby came and went EMU too.
It's full of contradictions - and upsettingly for some rose-tints on this forum - the railway and its nomenclature evolve!
And the service to Norwich is now similar to the service to Southampton and Weymouth - arguably more deserving of an 'intercity' service than the Norwich route.
And as for primary routes - will the WCML not be "IC" once HS2 opens? Even though it will still have Pendos and 80x? Is it about stock? Stopping patterns? City status? Catering? All nonsense.
Suffice to say that Chiltern will still need an outer-surburban/regional/mid-distance set up for its London-Birmingham services, and to compete on Oxford. As mentioned, it is and will remain the primary route to London for Banbury, Leamington, Warwick, Solihull (for now) and of course Bicester which is a huge draw and has a ton of house-building. EWR should see this building activity increase, same with Oxford Parkway.