As someone who is constantly on the road, having a built in sim card for connectivity is something I'm super excited about. This could be the 2016 MBP we wanted, but switching to windows still sounds difficult.
Why do you find that better than tethering to a phone? The last thing I want is a separate mobile account for my laptop.
Project Fi allows you to add extra data sims for free, so the cost is the same as tethering.