I don't drink coffee or any hot beverage while I drive. I only need a water bottle and that fits well into the door packet.
The problem I have is that I am a mechanical design engineer and things like this get on my nerves--I just got to "fix" it or at least try! So (this is where it gets really weird), I ordered a 3D printer last week and I am waiting for it to arrive! I have few projects that need a 3D printer and this E39 cupholders project is right on the top of the list.
You mentioned a good point about the drink temperatures affecting the AC control. I will definitely keep this in my mind when I start designing my own cupholders. Thanks for the tip.