Not an issue after 2018 of course when there'll be one island for up, one island for down for CX.
I wonder if any thought was ever given to arranging the Cannon Street platforms in the new layout so there'd be two islands with a reversible track in the middle. Would be the same track/platform area and make it easier on people in the evening peak!
Not enough room unfortunately - unless you take out a few escalators, but then the platforms would become unusable at busy times, which defeats the object!