Clive D. W. Feather wrote:

Right now the trains that arrive from the south on the western pair of
tracks use the eastern platforms, while those using the eastern pair
(the Thameslink ones from London Bridge) use the western pair. With the
increased traffic of TL2k this just isn't viable.

So Blackfriars needs to be turned inside out so that the Thameslink
platforms are the easternmost ones. Since their position is constrained
by the link to City Thameslink, this means moving the terminating
platforms to the west side which, in effect, means building a new
station *and* bridge across the Thames.

Thanks. I think then it might be cheaper to build new platforms over
the old piers (to the west of the station) for the southern trains, but
leave the existing station as it is, rather than demolishing the
station almost completely.