I'm in Australia, where the XPS developer edition isn't available, so we have to install linux ourselves, in my case, I've installed Debian Stretch.
BIOS / Firmware / Booting:
Suspend resume is slower than shutdown rebooting. The touchpad doesn't work after resuming. Hibernating - I'm not sure if this is working correctly, it takes a very long time.
All hardware is working correctly, it would be nice if there was an option to replace the bios firmware with openbios, which is far more powerful. The existing firmware is buggy and makes installing linux a battle.
The XPS 9365 is not formally supported with Linux. For suspend and resume it does not support traditional S3 (suspend to ram) but rather suspend to idle. Suspend to Idle is not well supported in Linux yet.
I would recommend that you change mem_sleep to s2idle (see github.com/.../states.txt for more information). This will force suspend to idle on the machine. You will run into a problem with needing to hold the power button for 6 seconds to wakeup, but wakeup will be consistent.
There is however work going on upstream that will be targeted at kernel 4.13 that improves the experience of suspend to idle to specifically address some of the issues you are (and will continue to run into). If you are comfortable running a development kernel, you can run Linus'es 4.13 development tree to get some of that now.