But that would mean that RMT shops could store their runes on fewer accounts, which would mean less revenue for Blizzard to keep the servers alive due to them not buying accounts for item storage.
Then there’s always the risk of an unknown dupe method being able to duplicate a stack of runes.
Probably not going to happen.
:o
Now, a dedicated shared stash tab, or “rune/gem bag” that stores say, up to 200 gems and 200 runes would be nice. Under the hood they’d store like they do now in cells, but the user interface could show them stacking. I would give up a shared tab for this. Buuuuut that’d be too much work for Blizzard to do for no-money-making D2:R.