Idea 1:
Create an interactive, physics pixel-based world with the elements of fire, water, wood and earth. Fire burns wood, water snuffs out fire and flows, wood rots slowly over time, and earth erodes slowly over time.
Idea 2:
Keep working on my previous project to add multiple colors and spectra of color across the lines when multiple people are interacting at once. Also possibly add different shards of color in the shapes created by the intersection of lines.