I think anything has to be designed and built with 5G/LTE in mind, Concentrate on getting it into the car and the rest will come, once its in there connection will not be an issue in 2 - 3 years, and anything that has been on the drawing board that long for Mycroft will be able to be deployed.
CES 2017:-Qualcomm CEO Steve Mollenkop: 5G Brings the Invention Revolution. start a 7 mins.
I envisage mycroft as a hub, and you will have a 5G connection to home to your hardware, if that is still necessary. I mean there's an android core so no it won't be soon.
It can be a pi with a wireless or blutooth connection to your ph, and whatever services that is capable of that makes it useful.
You will ask Mycroft for directions and they will appear on your navigator screen or HUD, and you will ask it to make a phone call or schedule a task for your home or public or private calender. Monitor your vehicle, does not have to be a car.
Sorry another long post. ATM I just want lots more skills. oh and a handheld version.