Do you know how well they work with Linux?
As you say, the 2014 is a great model - I'm using it right now, and it's plenty sufficient for everything I do.
I'm so used to HiDPI just working on my MBP that I never even realized it was an issue on the other OSes until I started thinking about switching.
No it doesn't. OSX in fact has a completely innane behaviour when a MBPr is connected to an external monitor. Meaning you have to mirror or put it in clamshell mode. You can't extend the monitor ontot he laptop screen. Works perfectly well in Linux for me.
Last time I tried this on Linux it was a mess, particularly when moving windows from the HiDPI to the normal and back.
If anything, clamshell mode is the buggy one - it has a tendency to go into or come out of sleep mode when I don't want it to.
I decided to give them another chance on the 4th gen X1 Carbon, and I've been very happy so far. The build quality seems much better, and they've nixed some of the annoying "innovations" from the 1st gen one (ironically including a touch bar at the top; they reverted to normal keys). That said, I've only had this one for about 5 months, so I might change my mind by the time another year or 2 passes.
I'm just a typical web developer, running a bunch of virtual machines, and an IDE. Any recommendations? I saw the Dell XPS 15 for around £1,300: https://www.amazon.co.uk/dp/B018FSX9GA/
Any others? I'm not a Linux diehard, so I'd probably go with Ubuntu.