Seems like Twitter is the best way to suggest ideas like this. I remember people requesting this feature a lot when the 3 came out. Thing is - there are prolly patents on this kind of feature and doing it in a way that doesn't step on them is tricky or they gotta pay for a license (my speculation).
I'd be happy to see this feature, in the mean time get a bright phone case that wraps around enough that you can see it on the charger .
When I first got my MY I left my phone on the charger and went into a store. Only after being in the store for several minutes did I realize what I had done. I nearly sprinted to the parking lot to retrieve my phone in a panic. Now, I just don't charge my phone in my car, unless I'm traveling long distances and don't want it in my pocket.