So a dead phone battery = unopened vehicle....Great

People are losing their smartphones all the time. I wonder what plan "B" is...

Wow a push button start, just like my 1931 Chevy has. Disk brakes like a 1950 Chrysler had. With the switches in the right place, you can use a buggy whip, do all the functions. With no batteries to worry about. Whats next a backup starter crank.

I wonder how this will tie in now with the freedom-grabbing attempt of the present admin trying to force Apple to build a back door into their iPhones software so as to allow FBI access to private information - instead of just letting Apple retrieve the info they want for them? Accessing peoples' cars at will would be open for anyone able to use the backdoor (no pun).

This is fantastic.
But there goes the Luddites again. The old 'lost phone' or 'dead phone' excuse. It's like the people who 100+ years ago said 'The problem with cars are that you could run out of gasoline. You can never run out of 'horse'.' Yeah, horses died too. And they got sick. And they got injured or stolen or ran away.
In this case the phone is just another 'key'. No different from what you have now, and if anything, more convenient because 1 less thing (your car key) to worry about. It has different constraints, but obvious benefits. People have their phones with them 24/7. You only need your car keys when you drive. And you don't know how many people lose or forget their car keys because people are not so obsessed by it. Everyone has to post about losing their phone though. So more people could be losing car keys than phones.

Smart phone battery life tends to not be the best. When battery technology matches that of the current keys, talk to me. Also, upgrading your smartphone can be a problem, as people often replace their cars with less frequency than their keys. IE: I could see an out of date OS, a bricked phone or a dead phone meaning an unopened car. This would be a fabulous opt-in thing, whereby one can still maintain a regular transponder based key as a backup, but eliminating the key entirely for a smartphone based solution is foolish.
Also, cue all the crackers and phreaks trying to hack into said system for fun and profit.

Could be better with a physical-key with a software-key alternative( phone or small dedicated USB/bluetooth device)

Great now they steal you phone and your car leaving you not only with no way home but also with no way to call anyone to pick you up.
Maybe if you live in a low crime area? Maybe somewhere other than the US.
And hackers, oh they would love to make their phone open your car, using a bit of malware. "But officer, I thought it was my car, my phone opened it."

So, that means if I have a smart phone I can steal your Volvo. Nice! Here you are 175 miles from home in a motel with your mistress and some dickhead with a smart phone steals your Volvo. Wonderful.

There should be a back up. I work large events, and there is always a few lost phones left behind. A bluetooth fob or fingerprint recognition system at least.