Splork the mxpExits variable still seems to be blank/broken.
I tried to use it to make a psuedo automapper a couple of weeks back... which leads me to my next point... a mxp variable to say what was the last direction you travelled would be useful...
It could also be used to script a command to "backtrack" your steps... really useful when you invent stupid classos without cleric and mage, and you get stuck in the middle of no where with no recall and no word of recall.
Of course that's never happened to me, because... because... erm...
Yeah, you can do it without an mxp variable, but involves making aliases for all the directions.... and trip traps you may enter to reverse properly.