I'll start with I'm not sure if this is the right place to post, please move to the appropriate place if needed.
I've seen clips of fgw HSTs diverted to Marylebone and Waterloo during times of disruption, also southeastern trains to Waterloo and Hull Trains to st pancras.
Are there other known...
Two things have come to mind after hearing this, will the world speed record (for a 3rd rail train) setting unit be preserved in some form?
Secondly there could be an opportunity for a conversion to a Pullman/Brighton belle/belmond style operation?
On many tfl and national rail stations there are already greater london rail maps with every commuter rail service (even southeastern high speed) within the oyster/contactless PAYG zone. Thameslink is unique as being the Crossrail 0,which merits it going on the TFL map (which is world famous)