This is already incorporated to some extent. Keeping in mind sets vary, Knight's profile is the L-shape. Rook has four parapets (and four gaps). Bishop has a

This is already incorporated to some extent. Keeping in mind sets vary, Knight's profile is the L-shape. Rook has four parapets (and four gaps). Bishop has a diagonal slit. King has 8 stubby protrusions in his crown. Queen has 8 pointy protrusions in her crown. Pawns are most basic (ironic considering their qualities are most byzantine). I guess it's nice to have a baseline piece for aesthetics.