@jon You need at least 7 407s just to run the trains to France as single units and would need 14 to run those as doubles (which currently is already impossible). The amount of spare 497s DB has is virtually none, and those it has will be in Frankfurt. If DB runs out of those spare 407s at any point, the service to cut is the Extension to Berlin because its the only service you can replace with another ICE.
This situation will only be rectified if the France-capable batch of 408s arrives ~2030.