So, I have left a good old trail of breadcrumbs on this matter
Dell “new XPS 13” dual booting Windows and Ubuntu Xenial Xerus
setting up the new 9360 to also boot Ubuntu 16.04
And in between, many updates and Ubuntu versions.
Until today, I was pretty happy with the device — I even extended the warranty, which Dell will do for you.
There was an issue on shutdown, where the HDD was apparently no recognised.
But who shutdowns laptops anymore? And the workaround was the canonical “yeh, thanks for the info” and then upon reboot, the machine was apparently fine.
It’s 2.9.0, so approaching with some trepidation, I download and install.
The installer works fine and at all times tells you what it is doing.
After: the HDD recognition issue is gone, along with some random noise on the USB speaker during boot.
However, the Windows partition seems to stick at some early point, for a warm boot.
A cold boot is fine and Ubuntu seems fine also on a cursory test.