Each card with different back could have happened if only all of the designers who had worked on the faces also submitted their back design as well. Unfortunately, not everyone make it... So, he worked with whatever is done. This new edition should try to compensate everyone and what the Unity Deck is supposed to be.
It's crazy on how.... when you thought it's just one deck... then quickly turns into three different editions, and then.... each edition has three different versions to satisfy certain groups: some that like holographic foil, some that like gilding bonanza, some who just want everything to be normal. I can bet, if there are no gilded versions, some people are going to throw a tantrum (assuming now people are accustomed to gilded decks on every custom design decks) and not going to back the project. Just be glad it is not 18 different editions (to comply with 18 different backs), which becomes 54 DIFFERENT DECKS (18 Basic - 18 Premium - 18 Ultra) if it happened! [your bank will question on how $700 gone in an instant XD)
This is when your completionism is tested: are you okay with just a set of gilded decks OR you are fine with just one basic deck OR you HOARD THEM ALL like a dragon.