Regarding the ability to send heirlooms cross-realms, please be aware that it's highly unlikely it'll be implemented during Mists of Pandaria as there're numerous technical hurdles that need to be overcome first in order to happen.
"numerous technical hurdles that need to be overcome"
Challenge mode Gear to be bought requires an achievement
Achievements can be account wide
1) Buy an item on a character, spending gold-honor-justice or whaever you want
2) Unlock a FoS
3) Log in with another character on another realm
4) You have the achievement
6) Profit !
Now the question is: "do Blizzard likes to get paid for realm transfers?"
"yes" -> there will always be technical hurdles that professional programmers "can't" resolve
"no" -> it's just a matter of adding a vendor and a FoS for every heirloom bought