I realize I may be opening a can of worms by asking this, but do you think the back should have a border?
There is a thread on that topic and I was arguing heavily in favour of borderless designs there (well, just that I'd like to see some more rather than designers having to avoid it due to so many people instantly dismissing borderless decks). For this deck, though? I don't think they should be a borderless deck. For me, your design makes great use of the white space and I think it would be jarring on the whole to lose that on the back of the cards. you don't need to go for any kind of standard border, though; it doesn't need to be a frame. I dunno, I just think that it's a shame that every single deck HAS to have so many millimetres of white space around each edge (and no more, either! No interesting shapes breaking off it, nothing!) or all hell breaks loose. this is supposed to be a creative medium after all.
Sorry, I'll just gather up the worms and replace the lid...
Anyway; I love what you've done so far enough that I'll probably buy them no matter what you do but I think the way your designs have been made on the front, the back would not suit a completely borderless design.