I’m not aware of any potential OSIs with Nine Elms. Battersea and Battersea Park is likely.
As for zone 1, it’s a nightmare. The developers who are part funding the extension demanded that it be in zone 1, but I’m fully expecting a new dual zoned sausage like the Stratford arrangement. Kennington to Elephant & Castle has to remain in zone 2. The problem of course is that 2 or 3 is the same fare in the Stratford area, whilst 1 or 2 is most definitely not.