As an owner of a previous generation XPS 13 I have a couple of comments.
> The battery lasts for 13h under Linux, which is not too shabby. However, it lasts a whooping 22,5h with Windows 10.
Not likely Dell's fault. User "aexaey" commented about this.
> WiFi performance is dismal in Linux. No problem with Windows.
There were some driver issues in my generation for WiFi but this was eventually sorted out. I would prefer Intel wireless cards over Killer since Intel typically has better Linux drivers but this is usually not up to Barton and/or the Sputnik team.
> The HDMI port on the separately sold docking station does not work correctly with Linux.
If this is talking about the USB 3.0 dock from Dell (http://accessories.us.dell.com/sna/productdetail.aspx?c=us&l...), this is because the underlying USB to display driver is from DisplayLink (http://www.displaylink.com/) and (last I checked) they have repeatedly refused to support Linux due to lack of perceived market demand. No USB dock is going to work with linked displays over Linux (that I know of/use DisplayLink under the covers).
However, TB3 docks do not typically suffer from this same problem. So now with the Sputniks coming with Thunderbolt, look at TB docks (you should be anyway) and this won't be a problem.
> The headphone port is very noisy with Linux. No noise whatsoever with Windows.
Had a similar problem with mine. Can't remember how I fixed it.
If you want to buy a laptop that has a team dedicated to supporting Linux on the hardware, you can't complain to much about Dell Sputnik. Dell has been doing good work and overall I think has made a positive impact on the Linux laptop/hardware support market. You are also more or less paying for support. It's a pretty neat thing to be able to file a support ticket with someone like Dell regarding a hardware issue on your laptop running Linux.
But this is still Linux we are talking about...and it is still very much a second-class citizen at Dell. So as long as you know this, I have to say I rather enjoy mine still.