Good news comes via andy who has sent word that an additional tab in your Stash will be available for purchase (in RoS) only however):
However, we do see a need with many of the additional crafting materials and items added in Reaper of Souls to add an additional Stash tab. In the next Beta patch, a new Stash tab will be available for purchase for players in the Beta. This tab will unlock in a very similar manner as previous tabs, and require purchasing the initial tab and additional 14 slot expansions over time. When the time comes for the expansion launch, this Stash tab will require the Reaper of Souls expansion to access.
The old hands among you will remember that 2 years ago the available stash tabs was reduced from 5 to the current 3 during beta testing but Blizzard said at the time they would review that and alter if player requirements changed and it seems they have and as a hoarder myself this is music to my ears.