I have a Toshiba p835-z370. It's a few years old but it still runs like a champ and all the hardware is supported on Ubuntu. Toshiba build quality is pretty good.
Aha! These seemed comparable with the Asus Zenbooks that came out at the same time. I've only seen one z370 in the wild though - what's the battery life like under Ubuntu?
Here's the teardown: https://www.youtube.com/watch?v=hMH0r76zdt0 . It's only upgradeable to 6gb though. Would love it if they had a 16gb upgradeable version.