I can't seem to find out what will happen to this section of track when
the DLR opens? I assume it will be closed as you can see the new DLR
section from the train.

The North London Line will either terminate at Stratford or be projected
up the Lea Valley line.

Crossrail plans to use the Custom House / Silvertown section (before
plunging under the Thames).

And I believe the Canning Town - Stratford section will be taken over
by the DLR extension to Stratford International.