I know this is just early days but I'd love to see this run through the tunnel so you'd maybe have a:

Hebburn to Cramlington
Sunderland to Cramlington

Services (the Cramlington bit has decent loads let's try and grow it) replacing the 19 in it's entirety in the process. It also should serve York Avenue and Calf Close Lane aswell imo otherwise it's just going to get stuck in the Tunnel mess for no benefits where you'd gain a link to Fellgate Metro. 

Would open up Cross Tunnel industrial links as it's impossible to get from Cobalt to Jarrow and beyond and it's impossible to get from North of the Tyne to Nissan currently and they're two major employment sites.