Paul Bowery wrote:

Has this ever been considered? Trains could run from
Barking/Whitechapel to Edgware Road and then on to either Hammersmith
or Wimbledon.

If memory serves me correct, a special Wimbledon-Edgware Road-Barking
service was run in the mid 1990s when Jubilee Line Extention work shut down
the southern side of the Circle. However it hasn't been adopted in more
recent years to provide a through service from Earl's Court to Aldgae East &
beyond in such circumstances - anyone know why?