An idea came across my mind on how to solve the problem with technical challenges making it impossible to have cross realm heirlooms.
Not knowing exactly what technical difficulties they are having, this is only a suggestion to bypass this if possible. Now to explain my actual idea.
At every racial starting zone, there will be a closet inside one of their main buildings, which can be unlocked. How to unlock this can be dscussed ofcourse, but either through buying access (XX,XXXg, earning a total of XX,XXX JP), an achievement, or a quest. When you buy a heirloom from the heirloom vendor it gets added to this closet, which can be accessed by all your new characters. The heirlooms here could cost a few golds (XXXg) per piece (which reduces the exploit by being able to get full heirloom when rolling on a new realm), and at the same time avoids you having to farm a complete new set of heirlooms on your 2nd realm.
Seeing as how the rep commendations actually work cross realm, adding vendor strings accountwide for each heirloom can't be impossible either.
Again, this is just an idea that crossed my mind earlier today and I wanted to share it with your, obviously there are certain areas where this can be handled a bit diffrently, but I just wanted to give you a general idea.