There is the rearrangement of the lines into Blackfriars to consider, and
some of the existing southeastern and south central routes are going to
become Thameslink through routes. In the peaks the through lines north of
Blackfriars will be at full capacity, so there is probably even less
likelihood of trains from the south stopping at City Thameslink, I would
have thought...

Paul S

Incorrect! South Eastern or Southern will not be diverting any of
it's services through the tunnel to the North. First Capital Connect
will have it's own services on the Midland and Great Northern
extended/diverted onto the Southern to places like Dartford, Ashford,
Sevenoaks, and the South Coast(Sussex)