One more thing: craftable parachutes.
If flight ever becomes an option for Cata, it should be a must.
Also, it’d just be cool to joyride a harrier jet or helicopter and bail somewhere, or do it by necessity at the loss of fuel or a collision with something.
Furthermore, the inclusion of flying vehicles would imply the inclusion of some sort of problem in air, to stop the survivor from ruling the entire world (at least without a fight) and discourage flight.
My suggestion, monsters that fly and are very hard to kill. Maybe even multi-tile flying monsters, because there would be plenty of space in the sky for them to move.
You could even have it so that these monsters stayed on upper z-levels only, meaning that they’d only be a problem for flying survivors.
And maybe this idea would also lend some use to the leathery wings mutation, other than negating fall damage.
I know that this idea is really out there, but maybe aircraft could even have an auto-hover setting, so the survivor could stow gear and whatnot in it and keep it fueled in the air while they raided on the ground, moving between z-levels on a hoverboard stowable in the back of the heli. Not a reasonable idea at all, I’m aware, but think about it.