Provide the same phone as a key operation on the S/X as is done with the Model 3. It should also handle multiple driver profiles, setting the correct profile depending on which phone is detected first (similar to fobs today).
Moderator: While this feature is already available on the Model 3, it may require new Bluetooth hardware and/or Bluetooth antenna placement to function on the S/X.
Using the phone app for the ModelS/X to unlock the car only works when you have cell coverage. If you happen to be in a remote area or in a parking garage where coverage is non-existent, then the app is useless and having the bluetooth option would be an awesome feature. The lack of bluetooth keyless entry was especially troublesome for me since my key fob goes through a new battery every 4 - 5 weeks, even after being recently replaced. The interim solution was to disable the auto-sensing proximity unlock feature of the car to prolong the battery life, requiring that I touch the door handles (or fob) to unlock the car. Since I never leave the house without my phone I'd rather have the bluetooth option personally.