I haven't played with the shift rule yet, but really like the concept! I'm trying to force myself to take a small break from programming, but it will be an interesting challenge! Adding shift will double the mathematical complexity, and so I may need to even run simulations overnight! Oh, and then of course adding shift to my digital version when I get around to it.
My guess is that the shift means that it's much easier to "escape", so like how p2 was favored when the first turn could move anywhere, I would guess p2 is favored in the shift variant. And for the cards left, I would guess that there may be more cases where there are no collapsed cards left at the end of the game. (aka p2 wins) Again, just hypotheses.