What's the hold up? YMMV but on my earliest XPS13 it came with 14.04 LTS I think and 16.04 LTS was just out, so I just installed fresh and it was fine with absolutely no issues: everything just worked.

As far as I understand it's a customized version of Ubuntu with some special drivers for the hardware. I was kind of expecting a system upgrade like Android or iPhone does, totally managed by the hardware provider.