Mizter T wrote:

The use for Moorgate - Farringdon I'd argue for is to retain at least
some of the track as sidings for use if and when Thameslink (and the
'upcoming' extension thereof, Thameslink 5000) went snafu. It would be
a useful place to put a defective train out of harms way, thus helping
with service recovery.

Isn't the reason for the deletion of the Farringdon to Moorgate line,
with Thameslink Millenium edition, due to the lengthening of the
Farringdon platforms to 12 cars across the Moorgate trackbed towards
the tunnel mouth. They can't lengthen the platforms the other way, due
to the gradient. So there would be no access to the old route from the
Thameslink lines. There would, of course, be the possibility of using
said area to extend the Met line sidings at Farringdon in that
direction.