It seems odd to buy a game because the developers added slots.
Asking players if Giants will be providing a free update will only get you speculation. Of course that's more than you'll get from them.
If you get lucky, you might see an update that provides more slots, but that would likely be it.
They are probably close to finishing the next version, which isn't much more than an update anyways, and it won't be free.
Happy farming in the new year.