Bigger is better!
You chose the wrong base model. Out with XPS13, in with Vostro 1720 (just do something about the sharp edges; they are really hard on hands):
- 17-inch form factor
- 1920x1200 display resolution (better if possible)
- Full-size keyboard and numeric keypad
- Traditional (i.e., with physical buttons) touchpad; make sure the user can disable tapping (this has been a bit of an issue for me in my Ubuntu exploits)
- Forget fingerprint authentication and the camera; if you can't, make them optional
- Ethernet port, if possible (there are still situations that preclude the use of wireless Ethernet)
- 8 GB RAM expandable to 16 GB (16 expandable to 32 would be even better)
- 128 GB SSD appears adequate, but some people might want the option of having a 256 GB SSD
- Make sure the hardware works with plain-vanilla Ubuntu (hey, if you pull that feat, it might work with Fedora, too!)
- No pre-installed tools or applications please! If you insist on having develolper profile, create an "basic" profile with no tools at all.
- An option to have Windows pre-installed to be run virtually would be nice
- Don't worry about support; if I can't figure it out, you probably can't, either :)