I've noticed that in Crusader Kings II you can select the 5K Retina resolution: 5120x2880. I did, and the game resolution itself was correctly set… but the interfaces were just downscaled. That is, they just had the same amount of pixels, which means that on such a high resolution, they were usually smaller than the ball of my trackball.
Searching around, I've found many mods who claim to enlarge the fonts, but do not actually work. And anyway I do not need to just change the fonts, I'd like all the interfaces to get bigger…
I guess the answer is "just no, lower the resolution", but maybe here someone comes up with a more creative and effective answer?