The ELL extension will actually see the line join the National Rail network, which will mean that it should actually increase the options currently available. The TfL blurb on their website even suggests that services will eventually run to West Croydon in the south and Highbury & Islington in the north.
Whether or not there are even any freight flows that could make use of this new route is a moot point, but even if there were I'm not sure that there wouldn't be restrictions that would prevent them making use of the line. For example, I'm not sure diesel traction would be permitted through Brunel's Wapping Tunnel or that such venerable sections of the route would be robust enough to withstand the pounding of heavily laden freight trains taking this route.
As for Liv St; no thanks. We're stacked out as it is, thank you very much. In any case, the new alignment is significantly higher than the old and the option to reinstate the old East London Junction has been ruled out because this alignment now rests peacefully under several feet of spoil.
O L Leigh