Well I don't own a shop but i have a suggestion for something the shops or at least one shop could sell. Sponges. Sponges suck in water within a 5x5x5. so you would be in the middle of the ocean but have dry land to walk on. I think it would bring more underwater homes and opportunities. Also, it can be used as an anti-grief block. If a griefer drops water on your house and you have sponges in the floor on in the structure, the water will not flow over the house. But they're down sides. Less squids will spawn and there is basically no chance that any type of zombie or creature will spawn in that persons house(unless they dug down). But they are a great decoration item and fun to mess around with. Please consider this suggestion. Thanks
http://www.minecraftwiki.net/wiki/Sponge
http://www.minecraftwiki.net/wiki/Sponge