I, like so many others, have been playing for a looong time on the same character. I have used lots of different gear sets. Most have been DE'd when new one came along, other sets were stored in bank (and later void storage). Some PvP elite sets, AQ set, old tier sets, some weapons (some of which are no longer obtainable), are now taking up the space of my void storage.
One could easily argue "just sell half of it". But I have done that, for most sets. The ones I have, I want to keep, and since I have been playing so long there's quite many sets I really want to keep. (inb4 you play too much).
Anyways, since Blizzard recently has been adding stuff to the blizz store and will likely keep on doing it (which I am fine with as long as WoW does not end up as pay to win) why not add extra Void Storage tabs for sale? It would certainly not be something everyone would need, or want for that matter, but there would surely be people willing to pay for it.
So would you consider paying for extra Void Storage tabs?
Edit:
People should also know that Blizzard has stated multiple times that their reason for not adding more void storage space is because of the costs involved. Yes, it costs money to add extra storage within the game (that is also one of the reasons enchants, reforges and gems are wiped when you put an item in void storage. The more stuff you have on an item, the more bytes of storage it takes, and void storage is kind of a cloud storage).
That is why we will not get more void storage space available for purchase by gold. Your gold is not worth Blizzard investing real money into upgrading the storing required by extra void storage space.
Hence, the only solutions would be paying actual money for more void storage, or that blizzard change the whole way you store items.