There have been extensive discussions about potential FTL mechanics for allomancy in the third trilogy, and a few about mechanical-driven allomancy (I haven't really followed all of those ones but one example is here). But it occurs to me that we've all overlooked the potential for very interesting applications of metal based magic in electronics: Suppose that in the third trilogy the Scadrians not only develop space flight but also artificial intelligence, that other great SF staple.
The abilities and/or personality of an AI could depend crucially on its hardware composition, either simply the native metals themselves or more subtly the presence of a feruchemical or hemalurgic charge. It's easy to imagine someone building their AI with a "heat sink" that instead stores sense-of-self, mass, or any number of other options.
One division (and often in-world question) in SF is whether AI in a given universe are alive/have souls. If Brandon chose to go with the "AI are people too" camp (which I think he would, given that everything has a spritual and cognitive aspect), then we could end up with AI displaying abilities in the metallic arts.
The above was my seed idea, and the one that I find most interesting. Still, I half expect this thread to be hijacked by related possibilities:
>One extension would be full-on androids, rather than the ship's-computer style AI. This type of story would focus more on the physical abilities than personality effects.
>Another extension (or maybe independent topic) is cybernetics. The idea of ability-enhancing implants has a lot of potential both in opposition to and in combination with the various metallic arts.
Then again, there could be enough room in a trilogy for all of the above. Now, there's an exciting thought!