After all trash and meltables are burned, next project: magma security.
The fire and magma men have hardly been a problem, but if I'm ever invaded by powerful hostiles who can fly through magma, I want better control over their approach. I've replaced grates with flooring since these magma channels aren't being used for what I intended; tossing refuse before it rots. The metalcrafts and blacksmith shops have both been converted to floor, with only one tile open beneath the forges. They may not be able to break through from beneath, but if one slips inside and starts wrecking, one tile exposure is more manageable to repair than a big open ditch.
Also sealing the top, since the mountain exterior is very poorly defended against flying attackers. In order to secure the whole magma sluice, I'm switching to a pump system that can be powered off the current central reactor. The armory and weaponsmithy are going to move downstairs, along with their smelters. A few more smelters will be added near the deathditch to expedite goblinite processing.
Crafts shops will be decentralized, with multiple shops around the first cavern, and the current aggregate will be converted to a gallery/zoo. At least until I decide to carve up the critters for food and leather, but I don't see a need for either in the next decade. They'll probably die of old age first, and then I'll see what new wildlife appears, or maybe I'll just slaughter them off to make that happen sooner.