That's how the Prius (and presumably all Toyotas) work as well. Actually, it would be a safety problem to have it work any other way. If the fob suddenly loses connectivity because its battery got low or it's been jostled behind a phone, having the car stop would be a big problem. I don't know of any car that works that way, does anyone?
First of all, battery warnings typically come months before the batteries go dead, but that's not all that important. The assumption here is that people don't throw their fob out the window when driving or chuck it through the sun roof. There's no reason for the car to do anything if it already knew the fob was in the car and it suddenly disappears. That's quite different from knowing that the fob was outside the car and that it never entered it, or knowing that it was in the car, the car stopped, the door opened, and it sensed the fob outside of the car.
Even though I've had cars that could go a moderate number of feet (I never tested it, but I did a web search just to verify others' experience) it was also a matter of not wanting to turn off the engine. It's a moot point with the Tesla. You aren't going to want to get out and look under the hood with the engine running, or not want to stop the engine when you simply want to toss something in the trunk.
Since I did have a need to have my fob in the car to start it, it was possible for the car to sense it when I opened the door, but momentarily think it was missing when I got in. One car solved that by having a slot for the fob, where it could read it using induction instead of battery power. With another, I'm frankly not sure what I would need to do. But with a Tesla, there are many ways around it if the car can't sense the fob once inside the car, but the driver had a way to get into the car. The app could do it. Punching a code into the console could do it, as long as you don't get it wrong more than a few times in a row. I did have a handful of times when it momentarily thought the fob was missing, but nothing that ever amounted to any trouble. And I still can't see why there's a need to have it drive away in the first place just because it knew that the fob was outside the car when the driver put it in drive.
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I find it somewhat disappointing. Mostly because I almost assumed it would include Valet mode. I would have also liked to have seen Spotify or Rdio baked in in the US also. But those aren't necessary and I wasn't fully expecting it. Of course Carplay support would be the Holy Grail for me, but I didn't even dream that would be in 6.0.
I'd like to see it too, but premature wondering about 7.0 isn't necessary. It might be in 6.1 and a few months away, or it might not. When Tesla puts out 6.0, it will have what they could reasonably have ready. It might even have bits and pieces of other features, but disabled since they weren't ready. I'd rather see 6.0 now than later, and if it would have taken until October to have it ready with Valet mode, I'd settle for getting 6.0 now and getting 6.1 in October or November with a few new features. Or not getting it then but still having what's ready now.