So, you've probably ran into a vault or two, and been cut down rather fast. You probably learned that this is because of the divine metal weapons. The alchemist skill still exists in game, so why don't we have a shop set up for making single bars of divine metal, amongst other things?
The alchemist would be given his order, "make steaming metal" or whatever metal you choose, he'll go to the shop, and you'll see a list of needed regents he needs when he's in the shop, like a strange mood, for that type of metal. Say, a bar of rose gold, some ash, flux stone, fuel, and a wood log. He takes these to the shop, and works for maybe a week game time. Then, you'll see an announcement in the bottom of the screen about his success or failure. It'd be totally skill based, just like crafting, with basic to superior percentage being failure, exceptional and masterwork percentage being a successfully created bar of divine metal. I can't remember which page has the skill to quality statistics, but if I find it, I'll put the numbers here. A legendary alchemist, therefore, would be just as important to a thriving fort as a legendary weapon or armour smith. For each metal, the needed items would always be the same for that world, with part of their generation being randomizing the items needed for the alchemist shop. In a different generated world, you would need different items for the same metal as the last world. This way, you can't just load up on what you need for a divine metal you know, and get it pumping fast. Also, you could have the option to make normal metals too, using other metals as the base. Say, three copper and a log for a tin bar. The alchemist wouldn't be a new forge, he'd work much slower, even at legendary, compared to a forge, and cost a lot more, but you'd be able to get metals you have no access to, such as steel on flux stoneless embarks. In their strange moods, you'd get batches of 3-6 of a divine metal.
So who's up for seeing the alchemist back, and actually doing something good for the fort?