I like your thinkin on that....ethernet might be a way forward. I suppose the only real advantage with a wireless system is that upgrading either end of the system becomes a software issue rather than a hardware one so that that I would not be restricted in the future by the cable bandwidth. (could also use optics but that might be pushing my luck
) The advantage of optic cables is that they are easier to protect against interferance - easier even than voltaic conductors.
I think you'll struggle to get the bandwidth out of wireless that you can get out of hard wired gigabit. Channel separation on 2.4Ghz means that you can realistically only run two or three channels in the same area, and the faster technology of 802.11n relies on bonding multiple channels together. What's more, a wireless system works much like the old fashioned wired hubs used to: Every packet has to be seen by every device. A properly switched gigabit network can give you gigabit connectivity between two devices while simultaneously giving gigabit connectivity between two others.
If you can find a car application that'll exhaust gigabit bandwidth, then you're doing pretty well. Standard definition DVD should run over 10mbit at a pinch, and presumably Hi-Def will have no trouble running over 100mbit in real time. Gigabit only really comes into its own as a network backbone or when shoving huge files from one client to another.
The wired Ethernet protocol should be inherently resistant to outside interference, as the balanced twisted pair transmission should receive interference equally on both wires, and it's the difference between the two that's used. Ethernet can operate in environments that generate a lot more EM activity than the car will. For peace of mind, you can always run screened cable.
The only thing that worries me about a wired system is the possibility of ground loops. I know these can be a problem in other automotive applications, but I don't know if it applies to Ethernet. Logic would say that it isn't an issue, as it's voltage differential between the two lines that's used for communication and a ground reference should be irrelevant. But don't quote me on that - do your homework first
While I'd primarily suggest wired Ethernet, I wouldn't rule out adding 802.11g or n support for remote access to the car's features. For example, you could use a Wi-Fi PDA to operate the central locking, remotely start the engine or activate 'see you home' headlights. You could even upload MP3s and video to the car while it's parked outside your house