Now, an ultrawide. That was truly a game changer in productivity for me.
Ditto. At one point I had 2x34'' Ultrawide side-by-side, but recently replaced with a single 49'' UW w/QHD.
Now, perhaps people are unwilling to wear glasses or contacts for very small vision distortions (understandable), but I do have poor vision, and I want even higher pixel density, because my glasses/contacts get me great vision (I get headaches if I don't correct to 40/20 or something).
We are reading paper books printed at 600 or 1200 dpi (though that often uses similar tricks to subpixel rendering), and nobody complains. As a matter of fact, people can tell a difference between 300 and 600 dpi, yet books are kept at, at most, an arms distance, so usually closer than most big displays today.
Depends on the UI you use. Gnome and tiling window managers should do it just fine. I prefer the macOS keybinds (including where full screen becomes a new desktop, combined with the "Magic Touchpad" gestures).
With regards to keybindings, one thing you can do is get ctrl/meta/alt in the same order as your Mac. Personally, I've swapped ctrl and meta on my MBP while I am using VirtualBox (with Kali) because that way when I'm in the VM I get local consistency. I usually SSH into the Kali machine from the MBP anyway.
With two 1920x1080 displays you can fit even more (or better 1920x1200). Also, what is the benefit of an ultrawide 2560x1440 compared to 2560x1440 or 2560x1600?
* More pixels -> more characters on screen.
* More characters on screen -> easier to glance between different parts of your code , open manuals, etc.
A 4K screen has 3840x2160 pixels. You could see that as either fitting 4 regular 1080p screens in a rectangular pattern, or just over 3 regular screens in vertical orientation (which is what you were considering).
Of course, if your current HD screen is only barely comfortable to you (likely), you will end up needing to buy a screen with larger dimensions (findable) to actually be able to utilize the screen to that extent.
Alternately, you could still go for that higher pixel density; in which case you end up with more readable characters. This does alleviate eye-strain!
Given enough pixels at your disposal (and a large enough screen), you can have the luxury of determining your own favorite trade-off between pixel density and amount-of-code-on-screen. You can do so on the fly, as tasks/whims/fatigue demand.
This is why -at least for now- I'd say you can never have enough pixels.
I'm sure there's a point of diminishing returns somewhere, but I think we have a long way to go before we reach it.