Considering how long it's taken to get all the relevant bodies (Network Rail, Lewisham Council, LOROL to get the Subway works done in the first place, negotiating with London Overground/LOROL over access to their footbridge for non fare paying customers would be pretty low down the chain when it comes to getting the much needed work needed on the neglected walkway.
I'd like to hope that most of the vulnerable pedestrians will have Freedom Passes (which incidentally are also given to disabled people under pensionable age) and for the rest of us that we'll have to tolerate this short inconvenience for the long term benefit for all users of the subway.