Ask HN: A Tetris variant with greater tactical and strategic depth?

In addition to the standard Tetris tetromino colors, squares can change to gray as a result of line clears.

If a line clear occurs without the line immediately above it also clearing, any squares directly above turn gray.

Gray squares cannot be part of a line clear and hence act as obstacles to line clears.

When a line is cleared, any gray squares immediately below it are removed.

What do you think of this variant?