I had this idea today, but its better to ask around before doing it.
A railway linking almost everybody, in a straight line, very fast, in order to quickly more from far away places. It would be above the ground, like y=100, or y=80, above mountains, so no problems with mobs. I did something similar in my single player game and its pretty good.
Then players can link their houses/places/cities to the main line, if they want.
So?