I don't think it'll be Gun Mage. It's a really minor class. There isn't anything wrong with Chemist just healing with Potions or the like anyways, though they'll obviously be more efficient and not rely on items in inventory, more like Alchemist in X-2. That and the guns shown so far seem pretty normal. It could be Gun Mage, but I have a hard time seeing it, and I can't see much reason to do that. Only issue I see is that Alchemist and Chemist are similar name-wise.