Been researching this for a while and I keep coming back to wanting a 17" laptop that can be my second monitor. The System76 Kudu looks like a solid option for a low end 17, but I'm looking more at the Oryx Pro with minimum specs lately because it provides a clear long term upgrade path. https://system76.com/laptops/oryx
It's not cheap, but being able to do monthly payments and being so well equipped in terms of ports (HDMI, mini display, USB-C, USB-3, SD, Gigabit ethernet) with a durable aluminum body as well as handling up to 64GB of RAM and space for 4 up to 4 hard drives (1 M.2/NVMe, 1 M.2, and 2 2.5" slots). I have a really hard time imagining outgrowing this thing via RAM/HD upgrades for many, many years.
Probably just a matter of pulling the trigger at this point. I also like knowing they provide lifetime Ubuntu support in case I did ever run into issues.
EDIT: After researching this a lot I ended up not going with System76. There were too many really bad support stories out there. After looking at it, I ended up getting a 17" Dell Precision via Dell Developer Edition laptops. I'll be the first person I know with this particular version, but the folks I know who have their XPS 13 Developer Edition absolutely love it. http://www.dell.com/learn/us/en/555/campaigns/xps-linux-laptop