I'm starting to see demand for an automotive-style wiring harness in the bicycle frame with standardized connectors for headlights, taillights, computers/navigation, and a few auxiliary outlets for cell phone charging and mini pumps. Power the whole bike off one battery - size of your choice - and massively reduce your chances of running out of charge on any one gizmo.

Electronic shifting would be a different ball of wax because if you wired it, it wouldn't be wireless.