I think it would be good to allow sponge placement in creative in exchange for cookies since the current deflooding mechanisms available to players only consist of (probably slightly glitch caboose) banners or just placing and breaking blocks.
It would be relatively difficult to implement though - having it just deduct 3.5 or 7 cookies per sponge placed would cause troubles if someone just spammed them unknowingly draining their account, and even rate limiting it to on per second would be suboptimal since that would cause issues because it isn't highly intuitive that placing them would deduct money. Another way is to deduct them from the survival inventory somehow, or keep a separate count of how many "classic sponges" they have purchased via /shop in classic or a command, or just have a command that places a sponge where you are standing - though it would have to be a short command.
It would be relatively difficult to implement though - having it just deduct 3.5 or 7 cookies per sponge placed would cause troubles if someone just spammed them unknowingly draining their account, and even rate limiting it to on per second would be suboptimal since that would cause issues because it isn't highly intuitive that placing them would deduct money. Another way is to deduct them from the survival inventory somehow, or keep a separate count of how many "classic sponges" they have purchased via /shop in classic or a command, or just have a command that places a sponge where you are standing - though it would have to be a short command.