More than likely testing things, yep.
They (Blizzard) do like to test things which i can understand.
As i mentioned in another thread, this bag space 'idea' i am pretty sure came from Diablo 3 which does increased space through a Seasons reward.
Nothing wrong with this as i see it.
Encouraging (or as some see it, a conspiracy of sinister proportions)) people to secure their accounts to reduce overheads (GM's retrieving stolen acccounts for one) is something to look at.