The problem with the X10 is the likely yield per passenger.
It's mostly concessions from what I've seen. Fare payers from Middlesbrough, Stockton and Billingham have deserted it for the improved Northern service.
Maybe it just needs to be Peterlee to Newcastle every 30 minutes with an hourly extension to Middlesbrough? Maybe even missing out Billingham entirely to speed up trips
RE: X10