You have to upgrade the CPU and then the 16GB memory option becomes available. (At the time of writing, the two CPU upgrade options are the i5-7300U and the i7-7600U.)
So XPS 13 has a similar problem where you need to buy the max CPU to get the 16 GB upgrade.
So comparing side by side..
XPS 13 with 512 GB SSD, 16 GB ram, i7-7560U CPU, 3200 x 1800 screen is about $1900.
X1 Carbon with 512 GB SSD, 16 GB ram, i5-7300U CPU (a touch slower), and 1920x1080 display, and force shipped with Windows (could not find ubuntu version) is about $2800
X1 does look nice, but not sure it is $1000 nicer than XPS 13.
I'm not sure if the link[1] will work, but there is a version of the XPS 13 Developer Edition with Ubuntu and 16 GB of memory for $1,949.99. I find the slightly largest display of the X1 Carbon appealing (seems like a good mid-point between 13" and 15") but it would be hard to justify the price difference, especially since it's lower resolution.
(The X1 Carbon 4th Gen had an option for a high-DPI display; seems weird that the 5th Gen apparently doesn't.)
