So what there would need to be is a license system. You dont need to buy them its based on how known you are in the server.
Say Android wanted to make a battleship, well we know he has no intentions to grief, and hes a known player, we all respect him, he would be allowed to make one and use the ability to fly it.
Say a new guy, just got whitelisted wants to build a small ship, he builds it and asks for the ability to fly it. Yotta or a mod goes to check it out, they see it looks strange and has a few spots ideal for TNT bombing.. He wouldn't get the ability.
I think bombing with TNT would be pretty cool, but it really just depends whos using it. If their using it just for griefing thats not good. They couldn't.
The ships moving isnt much of a big deal in my opinion, I mean sure, it looks strange when going backwards or sideways.. but its more about the ability to do so and how its being used. A trader ship in the shape of a circle would be awesome for those who care about the appearance of it when its moving.. But I think the true sight will be when we have an assortment of ships set up in a air port, in a city that isnt close to any large body of water. This would open every city for trade.
Also, there would need to be a set amount of how wide the certain ship can be built. Such as a trader ship, if you have a port for traders you want all the traders to be able to port there. As well as the ships will need to have some kind of rules when built, we dont want strange looking ships, like a giant wool platform with some cobble sides, it needs to look like a real deal thing.
Thats just my two cents

-asdf