With dev level access to a game Airships can be done with out breaking server performance. It all has to do with the coding solution used. If you played The Skyland Pirates server, or any of the airship plugin servers you know that the blocks moving causing problems, but that is only because the way they achieved movement was moving all the blocks in the server one space at a time. A more elegant solution can be seen with the airship single player mod. Essentially you can lock the blocks in place and make them a single entity that moves, and turns smoothly like a player does. Then you release control and the ship becomes blocks that are part of the world again so you can make changes.
In a game like this sight seeing is a big draw, but to be fair. If we do airships this will take away from the experience of walking and traversing the terrain, I know from experience on servers. You don’t see the same level of terrain construction, and development. Settlements become islands that you just fly to. One could argue that you limit airship travel by resources but that undermines the travel purpose unless the airship had some other goal such as combat.
