TfL plan to rebuild Bank to make it more accessible and less cramped,
starting construction in 2018 or so.

It strikes me that the easiest way to do that is to abandon the DLR
plaforms, and rebuild the DLR in a more east-west direction (east
south east to west north west, to be precise), near the monument end,
but stretching near (but under) the Waterloo & City platforms at the
other end.

That way, the northern line can be rebuilt to go deeper - to the
abandoned DLR platforms

The existing northern line platforms can become a huge concourse /
station offices / both

The DLR can extend west to ludgate circus without having to abandon /
fork from the route to bank. Admittedly it would have to miss out
cannon street, but the new entrance to the waterloo & city platforms
in the middle of walbrook should mitigate that (the entrance is
already going to be built once bucklersbury house is demolished, as
part of the Walbrook Square development).

The waterloo & city line would be able to be extended without blocking
access to it (because the new DLR concourse would still provide an
access route that could be easily used while they build a new one at
the eastern end)

And the northern line won't be in the way of the northern city line
being extended south any more.

But is that the best option?