Much of the post describes what we already know about this new feature: Collections will be somewhat separate from the items that they’re comprised of. In other words, the new Collections will have levels of their own.
And the collectibles you find will be automatically placed into their matching Collection–not in your Gift Box. However, any Collections that you’ve yet to complete before the change will be deleted, so turn them in quick before the change happens.
To put things in better context, Zynga states in the post the new Collections will work much like the Wishing Well feature in that there will be no inventory for collectibles any longer. They’ll simply exist within the Collections they’re attached to until you turn them in. Better yet, you will be able to trade in-demand collectibles with your friends. Can’t wait? Neither can we.