Never gonna be a thing, but it is still a good idea and its fun to think and talk about it. 
Sooo, you kill the DF and you get the furnace blueprint 50% chance. The other 50% is a blueprint for the BUCKET O LAVA. You carve it at the potter wheel (or alchemy why not) with normal stones, may be 3. Then you need to reach the lava pools and fill the bucket. Once it is filled it acts has a thermal stone. You want to carry more than one, fine, but may get overheated quick. You also need to use it radipely because once it gets cold, it solidifies and turn to stone. You can break it with a pickaxe.
What can you do with that you say? Well some kind of fancy lava lamp nothing really useful, just aesthetic. But the principal use could be a new type of wall/ torch. Its like a normal stone wall but with the bucket o lava on the top. You can place it, may be on a corner wall so it become a piece of wall that emit light. You can have it 2 and 3 wall pieces high ; what ever fit your needs. It emit low light, like lava pools, a bit of heat why not. And it is not ethernal, I'd say something like one season after that it turn to stone and you need to change the bucket o lava on top.
What do you think? Do you have any other ideas foruses of the Bucket O lava?