Well, I know it was guessed earlier (by ecNate), and it seemed like a spot-on guess. Here's the proof that what we are looking at is a big picture that is formed when you arrange all of the cards in a specific order:
The "low" hearts that have been revealed occur where stratosphere meets space. I believe these are in the upper-right-hand side of the mosaic, insofar as the grading of the 3H shows the demarcation between sky and space starts in a gentle curve from upper left to lower right, and the AH is all starry space (and therefore, the Ace would appear to the right of the 3H -- the fragment we saw of the 2H makes it obvious that it would fit between the AH and 3H, so that fits with this theory, and implies that the Ace is the upper-right-hand corner of the mosiac).
The lower spades are clearly high above sea level (mountain top on 2S), and while higher spades are also above sea/ground level, I still suspect they are in the second row from the top (and the lower spades and lower hearts are in the top row) given the shading of the blue sky... I believe the shading gets lighter as we get closer to sea/ground level. Witness 10S.
The higher clubs and higher diamonds are *at* sea/ground level, showing the city above the sewer system (9C), the boats upon the sea (7C) and the dunes above buried tunnels (10D). The lower clubs and lower diamonds are *below* sea/ground level, with the AC on the ocean floor and the 2D and 3D clearly deep below ground. Also, note that the right hand edge of the illustration on the 2D fits perfectly against the left hand edge of the illustration on the 3D. Since the 3D is to the right of the 2D, that means the Ace of Diamonds is to the left of the two, which implies that the Ace of Diamonds is the lower-left-hand corner of the mosaic.
So, yeah. There it is. A mosaic. A collage. A big picture.
And, as was also noted, there are a few other decks that did something similar, although none of them anywhere near as colorfully: The Escape Map deck from USPCC and the Unrest series of decks from R.L. Tomlinson (four different decks, each with a different "big picture"). The major difference I see here is that in the Pipmen World, each card has its own self-contained illustration as well as combining to make a larger picture, whereas with the others, the illustration part of each card is indecipherable without putting it in the context of the big picture. Plus, in those other decks, the big picture was in the background, whereas with the Pipmen World, the big picture is front and center.
I like it, and I'm looking forward to getting it into my collection!
This space intentionally left blank.