It would be an excelent way to balance servers who has a complex travelling system.
Also, it would be great if you could choose wich inventory slots should be empty to allow the waystone or warp stone use (the inventory, the hand inventory, armor inventory, Curios inventory, etc).

This would add some decent balance. It would encourage players to find other modes of transportation and only use waystones when absolutely necessary. Would work great with modpacks that add other means of transport, such as vehicles, mounts, or better railways.