Automatic Keyless wouldn't be too impossible. It would be the keyless start that would be a problem, since you need the key to unlock the steering column and turn on the accessories, or would have to modify the steering column lock so you could turn the wheel without needing the key.

I'm not aware of a complete kit you can buy, but making something wouldn't be excessively hard.

Make Magazine had covered some hobby projects where you would have two radio transmitters that would cause each other to light up when they got close. I think it was for some cutesy thing like teddy bears that would light up when you put them near each other.

You could use the guts of such a thing to detect when a keyfob is near and then unlock the doors as well as detect when the keyfob leaves and then lock the doors. Would be quite handy.

Relays could be used to also enable/disable the car's accessories when you got close.

 

Toyota Prius has it.

 

My mother's VW Touareg has it. She absolutely loves it. It will be a must have on her next car.

 

Corvette's have had it for a while now...

 

I called them about this its actually illegal to have that in your car here in the states i was WTF?
And the guys said yea i know, and canada's model has it.
We always get short changed on everything