I was thinking the same thing once I get the main gameplay loop together! It's often tough to determine how deep the 'holes' are until you get close to the point where you may be unable to recover. I considered either darkening the block colors the deeper they were located or adding a specific texture to the topmost layer of blocks, but ended up not having enough time.
My initial idea for the jam had much more to do with driving, having traffic and various tracks, more interesting car handling, and it would be a race to get to X number of rows cleared before an opponent. Ended up with basic tetris with a change in perspective.
Thanks for the feedback!