I'm trying to make a roller coaster system that uses messages but when in a mine cart it wont work i think this would be a cool feature. some cons: would have to only work on the res the minecart was placed on otherwise you could end up stuck in a minecart on a different res
http://track.emc.gs/issue/EMC-907 Definitely desired. The teleporting side effects is the one thing that has slowed this from being added. Will happen eventually though