I've been thinking for a while now one of the main conflicts for Era 3 will be North VS South. I swear I remember Brandon alluding to a cold war in E3, but I can't find the WoBs. Maybe I was mixing it up with the other potential cold war in MB - Scadrial vs Roshar in E4. Anyway, here's my two cents on where do we go now:
Tensions start growing between North and South. After all, the Southerners gave keep of a holy relic to a North-friendly kandra, and they destroyed it (from their PoV). Plus, there's the fact that Sazed sheltered the Northeners during the Catacendre and made them the rich and green Basin, while he did nothing for the Southerners who would have all died had Kelsier not stepped in. Basin which is, by the way, probably more attractive than the Southern frozen lands.
On the other side, the North feels threatened by this powerful neighbour who's been sending airships quite close to their lands without them even noticing, and who has access to really powerful technology in the medallions. And now they could be accusing them of destroying the Bands, which they had nothing to do with.
I do not think this would be enough to create a general pervasive mistrust between North and South, but it would be enough to create bellicist factions appear in at least one of the sides (wanting to subjugate/conquer/straight up exterminate a neighbour seen as a threat).
Autonomy sees the opportunity of having Scadrial destroy itself, and therefore supports these factions from behind the scenes, possibly without them even knowing. She also keeps triggering diplomatic incidents. (Kinda like what @JustQuestin2004 was suggesting earlier)
Sazed lets this happen, as he wants some kind of pressure on the North to make them catch up technologically, and the threat of a war with the South is exactly that. However, he can't really act against the deep reasons driving to the war, as he is still locked by his inner conflict. But he tries to lock the two parties in a stalemate, so that the war stays cold and everyone keeps inventing without actually destroying each other. The mass destruction weapons both sides now have are helping in that, by creating an equivalent to our world's nuclear dissuasion.
Kelsier is playing the fireman, because he also doesn't want of a war. Autonomy keeps lighting fires as quickly as the Ghostbloods put them out, and Sazed doesn't do anything because together the Ghostbloods and Autonomy's minions are maitaining the status quo he wants. Kelsier doesn't like that, as he feels Scadrial should rather go and get a lead in the space race now. He might try to start acting against Harmony? Not sure how it works with all his resources being directed against Autonomy. But he definitely wants a change in management.
So yeah, I think this is about where we start Era 3: with North and South in a cold war, and Kelsier, Sazed and Autonomy in a weird 3-way "conflict". Then of course, since those books are written by Brandon Sanderson, our main characters will do their shenanigans and turn this in an absolute chaos before book 1 is halfway done. I can't wait.
(Those are just my own thoughts, speculating based on just the content of the later W&W books. I haven’t really kept in touch with the fandom since TLM released, so I don't really know what did Brandon say recently.)
If this doesn't happen, I kinda want someone to write that as an alternate universe fanfic.
Edit: wow this ended up way longer than i thought