I had a couple of thoughts...
A folding key: the current one looks like something from the eighties and it stuck in my leg earlier in the week.
A more practical plastic used on the dashboard: the uncleanable and scratch prone plastic currently used is rubbish.
Lights on the stereo, I can't see it in the dark! Better standard speakers would be nice too.
I'd also echo some points made by others, such as audible central locking confirmation and "follow me home" headlights.
I then thought that, no, I don't want to see a single addition or improvement on the next model, as I don't want future buyers to get something as standard that I didn't! Selfish? Me? Surely not...
