I think this works. If your opponent doesn't tap all his lands at the end of his turn, you can target one at the beginning of your upkeep. However, if he does, then you have to destroy one of your own lands.

Could do with either (a) being bigger, or (b) saccing itself if you don't destroy a land.

Not very effective in either case, because it's a triggered ability that targets; the land's controller can just tap it in response so the ability's countered on resolution. This might be a rare moment when it's sensible to use a non-targeted ability: "At the beginning of your upkeep, destroy an untapped land of your choice."