What happened to plans to use it as London's centre for sleeper trains? Given (fantasy) proposals in another thread for cross channel sleepers, if combined with Highland and Lowland sleeper and Night Riviera (all of which I assume would fit into the timetable at such a time, could make it quite useful and result in only half of the undercroft area having to lose its "international" setup.
Alternatively, would it be able to be used to relieve Victoria (LCDR), or is there no capacity for that on the Chatham Main Line? My understanding is that Nine Elms Junction - London Waterloo still has some capacity (given the Windsor Reversible and Down Windsor Slow are barely used). If you re-signal so that the DWS and DWF become DW and UW and the WR and UWF become the UC and DC, the trackwork's already there and you have a flying junction already, thus removing any conflicting moves.