Neil Williams wrote:

So, here's a thought - during this period, to "back up" the Circle
Line, could the Wimblewares be joined to the H&C to operate through
from Barking to Wimbledon rather than breaking the link one stop short
of Padd? They're both C-stock, and both meet at Edgware Road. Are
there any other factors that are an issue, e.g. different train
lengths?

I seem to recall this precise combination ran on some engineering weekends
in the 1990s when the south side of the Circle was closed for work. So from
an equipment point of view there should be no problems. Timetabling may be
another matter.