To add another opinion, I'm really quite the fan of HiDPI displays but I found that 1080p is just about sufficient for my own 12"-13" ThinkPads. 96 dpi now feels limiting in terms of space and font fidelity, I would never consider going back after having worked with a higher resolution. It's nice to have smaller window decorations and taskbar without resorting to 6-8px fonts, and it really does feel so much nicer on the eye.
For a laptop and target audience like this, bumping it up to 1440p probably makes sense in the next iteration. It's also important to note that there is a trade-off of more quickly depleting battery with higher-resolution screens. It sounds like the battery in the Librem 13 is just about par (if even) with current runtime expectations for Linux, bumping that up to 8h would be qualitatively a much higher jump for me than increasing the resolution.
That, and going 14" with a thin-border "infinity" display. Also, can we please get the Lenovo key arrangement for arrow and PgUp/PgDown keys? This continues to be a deal-breaker for me with most laptops.