I watched a video for the Plane mod on youtube and it looked absolutely awesome! I'm not sure that planes would fit in with castles but i think it would be pretty awesome to have something that enables faster travel without teleporting!
What also appealed to me was just how many materials you need to collect to make a single plane! Things like that always feel more rewarding as you really have to put some effort into obtaining them.
Fingers crossed Mojang add something like this to the game in future releases!