It would make sense to not keep everything running, that's for sure.
On the other hand, I don't understand why they have both CDG and CGN in the same time. Those 2 are very close to each other. Why not concentrate everything in a single point ?
The "funny" story is that TNT left CGN 10 years ago to come in LGG because it was a much better solution. Isn't it still now ?
It happen that the location of LGG is just perfect, in the middle of CDG and CGN and in the middle of the european most crowded area. And they plan a high speed train cargo link between CDG, LGG and CGN : the carex project.
EURO CAREX : Cargo Rail Express
Everything is almost too perfect.
The main problem is maybe free space. There are plan though :
Liege Airport - Mass Plan Evolution