Honestly it'd be really cool to add objects that can sometimes spawn within the tetras to mess with the piling of the sand.
I imagine boxes, gems and bombs of sorts, all of which activate when any sand touching it is cleared. Boxes could have extra points, score multipliers, and stuff, maybe even sand of another color that can't be interacted with until the box is gone. While bombs would clear a circular area of sand when triggered.
Mostly to lean into the motif of sand in the desert.
Also it'd be cool to have modes with different shapes than tetras or a wide map mode for more chill gameplay