A few fictional services I've had in mind are:

219: Peterlee Bus Station - Shotton Colliery - Wingate King's Road - Vicarage Estate - Station Town - Hutton Henry - A19 - Wolviston - Billingham - Norton High Street - Norton Road - Stockton High Street - B6541 - Middlesbrough Bus Station
Basically similar to the old 211 route (https://www.northeastbuses.co.uk/bygone/...st2009.pdf) but additionally stopping in Shotton Colliery, Hutton Henry (in both directions) and Stockton.

X90 (coach service) - Darlington - Newton Aycliffe - Rushyford - A689 - A1(M) - Bowburn - Shincliffe - Durham University - Durham City Centre - Framwellgate Moor - Chester-le-Street - A1 - A184 - Newcastle Coach Station
Basically gives Darlington and Newton Aycliffe a direct bus link to Newcastle. The number comes from the service from Darlington to Newcastle previously run by Stagecoach (https://www.northeastbuses.co.uk/bygone/...st2000.pdf). Would also work as a faster alternative to service 7 between Darlington and Durham, and gives Durham University and Bowburn a direct service to and from Newton Aycliffe and Darlington.

89 - Bishop Auckland - Coundon B6287 - Leeholme - Windsor Terrace - A689 - Rushyford - Chilton - A689 - Bradbury - Sedgefield - A689 - Wynyard The Meadows - Wynyard Wood - The Wynd - Wellington Drive - Wolviston - Billingham - Marsh House Avenue - A689 - Greatham - A689 - B1277 - Hartlepool Victoria Road - Hartlepool Marina
Gives Chilton and Sedgefield a more frequent, more direct link to Bishop Auckland. Also gives Sedgefield a link to Billingham and Hartlepool, and gives a link to Wynyard and Wolviston, which do not currently have a regular bus service. The route number "89" is derived from the A689, and is a separate service from the existing 89 from Bishop Auckland to Escomb.