If the durability is up there with the Thinkpad series of old I could see replacing my current machine with one of these.
To the best of my knowledge and experience [0] the scaling isn't any different across any of the major GTK-centric DEs (GNOME, Unity, Cinnamon, Pantheon): You get integer scaling factors for the entire UI, and a separate text scaling setting, both which work as expected, with a possible exception of a few multiple-versions-old Qt applications that might respect neither setting. They are rare in my experience.
I find that on a 13-14" laptop at 1440p this is insufficient. No scaling (1x) is too small for my poor eyesight, but 2x scaling is too large and wastes screen space. I forget where and how long ago I encountered a Linux environment with 1.5x scaling. Maybe I dreamt it, but 1.5x was just about perfect.
My current strategy (14" Thinkpad, 1440p) is to keep UI scaling at 1x, font scaling at 1.5x. This works for most applications except for web browsers (where the font rendering size is not dependent on the system font settings). In browsers, I will use a plugin that sets the default zoom to 1.5x, basically bringing everything up to the same experience.
I can imagine that a 15" laptop with thin-bezeled 4K screen might have the same challenges as 14" at 1440p (i.e. a 1.5x scaling would be ideal, but does not exist). However, this is only a guess, based on my trying a full 2x scaling on a 13" 4K display. It was actually nice, at 15" 4K it might be sit in the awkward zone of 13" 1440p: too small at 1x, too large at 2x, with no single setting for a 1.5x sweet spot.
[0] I install new versions of GNOME, Unity and MATE at least once a year to see if one has surpassed the experience of my current preference (Cinnamon).
xrandr --display eDP-1 --scale 1.25x1.25
xrandr --panning <new effective resolution>
Unity is about on par with Windows, in my experience. So it's usable, but not great. You'll probably run into programs that don't scale well, but if you spend most of your time in an editor, terminal, and web browser you'll be OK.
In broad strokes, yes, the XPS13 (and 15) are pretty close to the Macbook Pro's. However, since Apple has already been 'here' ( = great trackpad, solid body, great battery life) since 2012 they have had time to absolutely perfect the Macbooks. Just a small list of engineering stuff they did:
1. Battery life. They developed both terraced batteries and special non-standard sleeper modes on Thunderbolt chips. Also one of the few laptops left that has a 'muxed' dual-graphics solution. 2. Custom motherboards, in very weird shapes, to maximize spatial efficiency. 3. Fans. The fan blades are all at a different angle, thus producing a slightly different pitch and spreading fan noise across the audible spectrum 4. The hinge. Opening and closing a Macbook is an absolutely joy, because its sturdy enough to not wobble, but if you open it, it doesn't tilt the Macbook off the surface. [1] 5. Magsafe (sadly gone since 2016 models)
The XPS line not having these little things is not a show-stopper, but IMHO does elevate a laptop from 'great' to 'near-perfection'.
[1] They test this painstankingly, so it feels perfect from the 11" Air all the way up to the 15" Pro. Even my dad's brand new 2016 XPS 15 still has the tilting problem.