Ok let me explain less conspirationally.
The Borders line was built in the early ‘10s for two prime reasons. 1) to win votes in the Scottish Parliament in the Borders area, and 2) to test various procedures in the Scottish Parliament. The business case, as is well recorded, was shaky at best (but better than most reopening proposals), but it was much more a political reopening, not an economic one.
Clearly the procedures don’t need testing now, and also clearly, there are no votes to be won in the Scottish Parliament from building the line through Cumbria. Also, the business case will be nothing short of hopeless.
So without the politics, and no economics, an extension into England has no chance.
And it would have to be a national issue, if it was to have any chance of gaining consent to build it. Which is another reason it won’t happen.
I must say I am at a complete loss as to why any money is being spent on even doing initial feasibility.