A role which previously the North London line filled. *The Jubilee
Line is an expensive replacement. *By now the North London Line to
Docklands would have been an Overground Link.

The North London Line in that part of town was okay if you wanted to go to
north London and if you could bear the infrequent service it was fine for
Silvertown and North Woolwich. But it was utterly useless for getting from
Stratford/West Ham/Canning Town to places south of the river. The
development in the docks was not adequately served - even three car DLR
trains are still slow (and the Waterloo & City heaving at the other end) and
no great substitute for a proper tube lin to the centre.

Which is why I believe the NLL needed to be diverted from Silvertown
and North Woolwich, and instead run under the Thames to an interchange
with the Dartford lines. *There would nothing to prevent an
interchange staion with a Jubilee route to Thamesmead.

In my eyes, the ideal situation given hindsight would have been for
the NLL's Poplar branch to have been renovated and tunnelled under the
river as the DLR was and linked to a rebuilt Greenwich Park branch,
which would then run through to Clapham Junction via Peckham Rye.
Likewise, there would have been little need to wait for Crossrail to
run from North Woolwich to Abbey Wood had the NLL been extended the
same way, with a service from the North Kent line running via Canning
Town and Stratford to the Goblin at South Tottenham, thence onward to
Willesden Junction and Richmond.

Given the demand between Stratford and Canary Wharf I believe a grade-
separated curve linking the two Crossrail branches would serve this
demand far better than the Jubilee line does, and it would enable more
use to be made of the capacity on the two branches (i.e. every train
to Canary Wharf from Whitechapel is a train to Shenfield that has to
use up capacity at Liverpool Street). Accordingly, the Jubilee could
then have it's branch to Thamesmead, with the DLR running alongside
the NLL up to Stratford.

....swinging back on topic, the Northern Line extension to Battersea
couldn't be more of a pig's ear if they tried, and funding it with a
loan is disgraceful. The capacity of the CX branch should be used to
extend south east, e.g. down to Crystal Palace via Loughborough
Junction, Herne Hill et. al. en route to the Hayes branch. A major
redevelopment of the drain (including lengthening the existing Bank
platforms to 8 car length and building new ones at Waterloo) would be
the ideal way to serve the Battersea area, with stations at Bank,
Blackfriars, Waterloo, Lambeth, Vauxhall, Nine Elms, Battersea Park,
Battersea High Street and Clapham Junction, with depot facilities
provided by London Road (the Bakerloo getting a new depot on its own
southern extension.)

Even if you accept that the drain proposal above is dependant on the
Bakerloo works to free up London Road, then simply building Clapham
Junction to Vauxhall then linking to Kennington is the way to do
things for the time being so you can just reuse the infrastructure
later in doing things properly. Likewise, the reasons given for not
interchanging with Vauxhall are bunk of the highest order. Routing the
line as required and hollowing out the platform tunnels is all that is
needed for passive provision until Crossrail 2 relieves the Victoria
line enough to permit the interchange being brought into use.