This would propably be a good idea for creative or servers where they want to create a nice spawn..Therefore i believe this should be added eventhough obtaining huge quantities of mossy cobblestone on survival is a tough ordeal..
No, it's not hard. Even if it's hard to find, once you find it, you get a lot of it.
Anyway, I support. I mean, you can get mossy cobblestone walls. Not sure about the bricks though.
actually one could craft mossy stairs and slabs from mossy cobble. and MCMMO servers have the whole green thumb thing.
plus it would look great in future generated structures, as well as strongholds and jungle temples.