I just thought of something. I know the full USPCC prototypes are very expensive, but if you just wanted to see what the back design actually looks like once printed on cards...
Can the 15$ or so custom bicycle decks be printed full-bleed? You know, the ones that are marketed as gift/promotionnal, you can get them printed with photos in the back or whatever image you want... But I don't know if they have border restrictions on those.
Oh, and I know I'm supposed to be thinking of the Wonderland deck, but I just had a quick idea for another design that would be very simple, but unlike anything that has been done so far. Here's a quick question. Can you get metallic ink in any color? If the answer is yes, I might be in for some real innovation.
You can check here:
http://www.bicyclepersonalizedcards.com/But it doesn't look like you'd be able to use this option for a full-bleed print - just a simple photo or image repeated on the card back ad infinitum.
Try this instead:
http://www.809bicycle.com/You can order custom print Mandolin Back cards - where you can alter 100% of the front or back except for Jokers or Aces of Spades. If you just want a single back and a single front design (as if you were printing a gaff card to sell), $300 gets you 5,000 cards. You can use the Alice design on the back and put a business card or something on the front. That's the cheapest way you're going to get to test a back design as far as I can see.
I'm actually considering this for when I create business cards for myself instead of using custom-printed cards straight off the inkjet printer I have at home... I want to upgrade to a larger PO Box before I do this, and any kind of address change is a headache, even if it's from one PO Box to another. I may keep the smaller one running 'til the contract runs out in March and get the bigger one now to ease the transition - but I digress...
You can place orders for decks as well, but they cost more. However, the Mandolins in a custom deck form can be ordered in smaller batches than Rider Backs, saving you some cash.
As far as metallic inks - I see no reason why more colors wouldn't be available. What is an ink color, after all, but a mixing together of other colors?