Well, to get it, I had to follow some easy steps.
1) boot Icaros and update system files to a fresh build
2) choose any old VESA boot menu line
3) change VESA=1024x768x32 (or whatever) to VESA=1920x1200
4) press Ctrl+X
5) edit boot/grub/grub.fcg to have this always available
Icaros users should wait for 1.1.2, which hopefully will have this feature already included. If you can't find a matching resolution for your nightly build, please read this thread on Arosworld, it gave me the right hint!