The problem with them making a wood type is that so many pokemon suitable for that type are already grass types, which means they would have to change a lot, including adding new stats, weaknesses, immunities, and advantages. And someone mentioned sudowoodo being eligable earlier. Well sudowoodo is a ground type, and its name means "Fake Wood" because it mimics a tree, so it would not be suitable for this type. I dont know about wood, but i would like to see a light yype pokemon group as well because they have dark already