I love the Shift variant, it's the layer of complexity and strategy that I think Collapsi needed. Now it's not just a game of trying to find the most optimal path and surviving until the opponent runs out of moves, it's also about creating new paths or blocking your opponent and disrupting their plan.
It would also be cool to have "Shifting Puzzles" on the Solo mode where you have to shift a row/column each turn to be able to solve the puzzle.