+1 this would be really useful for WOF probably
Gamerule Idea: Eggshell Chess

I have a suggestion (a variant similar to eggcrack), which I call Statue chess.
Fully cracked pieces get frozen rather than dead (i e., they can't move anymore). This variant willl have different dynamics from eggcrack. Here, king can also have cracks. One interesting special case is when only kings have cracks and kings can heal by capturing opponent pieces (amount of healing proportional to the value of piece king captured) or by staying on the same square for a number of moves.
cos what goes up must come down