Jamie Thompson wrote:

On
a vaguely related note, when the Northern line gets upgraded they're
going to find themselves back in the 1930s again...namely they'll need
room for a lot more trains with no obvious contenders for stabling on
their existing route. They may well come to regret selling of the
Aldenham Bus facility (redeveloped from the Bomber Factory, itself
developed from the unused, abet completed, Bushey Heath Depot) in the
1990s yet. They may have to revert to the unfavoured alternatives such
as Mill Hill (aka. Copthall Sports Grounds) or Edgwarebury Park (aka.
Brockley Hill Station's site), so they'd both be quite good green
spaces fights), or expanding Highgate Depot by cutting down lots of
the trees in Highgate Wood (again, that'll be a nice political bit of
environmental fighting).

The alignment from Edgware to Edgwarebury Park has been built upon.

There seems to be room for enlargement just south of Edgware.