I was pondering a map the other day, and I noted quite how close
Moorgate and Cannon Street are. I guess the city widened lines to
Moorgate are a lost cause due to the planned work at Farringdon, but I
wondered whether it has ever been suggested to extend the Northern
City Line south of Moorgate and link up with the line at Cannon
Street, making Cannon Street into a through station. This would
allow, say, the extension of Northern City Line services to London
Bridge and points onward (possibly as part of the Thameslink network?)

Has this ever been suggested? Are they any especial difficulties
apart from the sheer cost of tunnelling in EC2. (Bank of England
vaults?, I can also imagine the gradient being a problem)?

--
Abi