Charles Ellson wrote:
The DC line is part of what was built as a network of lines with
common equipment and working arrangements

Whatever gave you that idea? The Silverlink Metro is a mess of
orphaned lines built by countless different companies that have been
munged together to form a very mixed up network. The only line the DC
line was built in conjunction with is in fact the Bakerloo.

As far as rolling stock goes, TfL haven't ordered enough 378s to cover
all lines and provide an improved service, and they'll take several
years to all arrive. I wouldn't be surprised if the DC line never gets
378s, and goes straight to modified Victoria Line stock, which will
become available around the same time.

U