Paul Corfield wrote:

I'm not at all certain about what is planned but doesn't Farringdon
Crossrail station end up being "double ended" with Barbican? Would
the Crossrail construction for this take up part of the abandoned
Thameslink alignment thus rendering any use of it as sidings or
running track pointless?

I have a vague recollection that the Crossrail escalators at Barbican will
cut through the former Thameslink running lines.