The first gym is definitely going to be bug-type. Its badge is shaped like a beetle, so, yeah. Second gym—I'm expecting it to be focused on fighting. The badge symbolize bricks, which fighting-type Pokémon are related to. Either that, or it could be a rock gym, just like the way it's been mentioned before. I'm not exactly too sure about the third gym… perhaps it could be steel-type? d: Fourth gym is based around grass, that's for sure. Its badge looks exactly like a leaf, and it's colored green. Fifth gym might be electric, maybe.
We've never had any dark-type gyms before, so there's a high chance that we might get one in this generation. A lot of people want it, too, which is a good reason why GameFreak would at least want to consider having one around. For this reason, I'm guessing the sixth gym would turn out to be dark-type. The badge could indicating the "dark" of the moon, possibly, which would fit the gym just perfectly. The seventh gym could end up being poison, since the badge is in shape of some sort of a fog, which poison-types associated with. As for the eighth gym, I don't really know, what type it could be, but I hope that it's fairy. :)