I understand pixel density is nice, but for the vast majority of workflows you do not need anything better than 1080p on a 15" display.
http://penguindreams.org/blog/msi-ws60-running-linux/
My current Dell XPS15 does as well; both ran/run Linux. I do a lot of photo editing (Lightroom in VM, although I'd started to use Darktable) and I probably wouldn't buy a primary laptop without a UHD display today.
But it's not a requirement for 'most developers' - in fact the ones I know with high resolution laptops don't want them, they're just annoyed by lingering issues with UI scaling and tiny text. I can't think of a sane reason for having font sizes so small that you need 4k to display text properly. Text is plenty crisp at 1080.
Also this is a laptop. More pixels means shorter battery life.
Maybe what you really need is a desktop.
It looks so much better at 2000. Of course you can get by with 1080 - hell, there've been times when I got by with 600 - but when you can see more code and read it more easily, it's easier to get on with development.
Obviously, nothing. High resolution for most people is still just a 'nice to have.' But even 1080p@15" will produce relatively crisp text. I'd argue East Asian languages are the only ones to significantly improve in legibility, as sub-pixel rendering pretty much does what it needs to do for English nowadays.
That being said, I absolutely will always go for high DPI and everything, I just don't think it's sane to argue it's an absolute must for what amounts to typing and reading text.
<FourYorkshiremen> Eeee, you were lucky. My first personal computer maxed out at 320x256, or 160x256 if you wanted more than 4 colours. </FourYorkshiremen>
LUXURY. We had 32x24 b&w characters and we were glad of them.
(ZX81, nominally 256x192 pixels but only accessible as 8x8 character cells.)
edit: seems like HN doesn't support these characters but see https://en.wikipedia.org/wiki/Block_Elements
I made a 'zooming through a tunnel' program in assembler once, using them
Although in the context of developing on small screens, they're not very helpful.
(And if you redefined the character set on the fly, you could make things like Forty-Niner. https://www.youtube.com/watch?v=OTTWMIQVznM )
In the manual, there were some programs you could type in, including "Mars Lander". The calculator shows a landing speed (e.g. "8.2") and then you need to type the thrust adjustment (e.g. -1.0 or +3.0) and then the new landing speed is shown. If you do it right, you land safely and it shows "00000" or something. But nah, that did not happen, you just crash ("11111")
Following that, when I got ZX-81 with 32X24 screen, and like, 1Kb of memory, I was in heaven :)
Reading those on a large (9") tablet is doable, in 1-up portrait mode. Reading on a large retina desktop display works -- 2-up mode with excellent resolution.
Reading them on a laptop suck balls. At a 9:16 aspect ratio with 1080 px height, both font and resolution are too low to read clearly. And unless you've got a hybrid laptop (I've been looking at options online, but they strike me as overly fussy and asking for trouble), no-go.
At a higher dot-pitch, this might work, but it's pretty iffy.
Surprisingly, other than the OS and applications, a tablet makes a suprisingly good mobile device. Samsung's announcement that they'll be supporting Linux installs is promising. The other side of this that needs addressing badly is standardising keyboard and case form-factors.
A tablet (display + brains), self-supporting folio case, and bluetooth keyboard isn't quite perfect, but it's quite good. In reality, keys are falling off and/or getting disabled on the keyboard, the tablet itself cannot run a real OS, I'm fighting Android, and virtually the entire App ecosystem is worse than useless.