I think it would be cool to see a mob similar to Doom Gaze from FFVI.

For those who are not familiar, Doom Gaze was a boss that you encountered randomly while flying the airship. When encountered it would escape the battle after a few minutes and move to a new random location but would not regen (kinda like the Twinkling Treants from a few years ago). In order to defeat it you would have to find it and fight it multiple times.

They could just use an amphiptere model and have it attack the airships randomly. They could give it massive HP (like 500,000 or so) so that it would take multiple flights to lower its HP enough to kill it.

If nothing else it would give people a reason to use the airships again.