It could, and I believe that devices designed for that very purpose actually exist 'on the shelf'. If done properly, the device needs to be clever enough to know whet to do in the (unlikely) event that the two showers were switched on simultaneously - I think usually by giving 'priority' to one of the showers.OOI could a contactor be used to switch between two electric showers, thus saving on an additional fuse/rcd etc, and avoiding problems with overload at the CU?
Strictly speaking, I think that one needs DNO permission to connect more than one electric shower to a domestic installation - and I suspect that if such permission were granted, they might insist on such a device being fitted.
Kind Regards, John