Boltar wrote:

Rather pointless terminus = area that is already served by mainline
trains
to liverpool street, NLL, central line & DLR. I'm trying to think of a
reason
that a run down tip like stratford would need yet another tube line to
go
there.

How about so that NR passengers from the huge commuter hinterland of NE
London and Essex can get to the equally huge centre of employment at
Canary Wharf without having to go into Central London or use the DLR's
pretend trains?

(I imagine providing access to the Dome from aforementioned areas also
had something to do with it...)