I'd like to see some more Water birds, especially some more bulky ones, since I like the Water/Flying combo. If GameFreak will do it I guess that they might probably base it off a Gannet or a Booby or something else like that.
A steel ram also sounds cool, and I hope something like that will come up in the X and Y series. Maybe it will be able to learn moves like Iron Horn or Bovine Toss.
I wonder, maybe there will be a Dragon-type Fossil Pokemon (In other words a Dragon/Rock type). Now that's an example of the ultimate prehistoric Pokemon! (Might even exist before Arceus was made.)