>>2043078
>the safety systems are different and incompatible with each other
Surely they can make the trains compatible with both with minor retrofitting, or standardise the systems, trivial compared to laying an extra 100km of largely underground track.
>maximum capacity
Just do what JR East does and make two trains kiss and split/join them at Maibara, (ideally also make it so they don't decouple while in motion)