Boom, indeed. It'd be a particularly nasty weapon if fired at a pack of thaumavores like the Whisps; they'd absorb a tremendous dose of aether, overload, and detonate in fallout reactions pretty much at the same instant as the pulse shreds the world, making it the equivalent of a radioactive blast. Go to Comment
I think the worst component of this would be for the soldier at the epicenter, witnessing the ripples preceding the event, and realizing he's too close to the heart of it to escape. The kind of sudden fear, panic, and apathetic despair that would have to crash over him in that moment would potentially be as destructive as the weapon itself; I imagine some commit suicide before the detonation occurs, if they know what's happening. Go to Comment
You're correct; I imagine mock assemblages of components would relatively common among the less-prosperous states, leading to a kind of cold-war state where everyone distrusts everyone else. Ulfdin likely has a top-grade counter-spy network in place to protect their control over the key components of the devices, and that there are probably those among their welathiest rivals trying to reverse-engineer one of the cannons in order to create their own...
They are, indeed, fairly expensive; given their sheer bulk and come delicate components, they're not battlefield-portable, so they tend to be emplacements. Ulfdin tends to see a fair surplus to their treasury whenever one gets comissioned, as they have the secret of growing the 'warp crystals' that help focus the transformation effect. I expect other nations are vigorously researching the method of creation, but as the sub suggests, it involved less than pleasant methods to divine the secret. That said, it's only a matter of time and will, and I'm sure that eventually you'll have battlefields that have soldiers equipped with firearms equivalents of Uther Doul's Possible Sword, each firing producing a swarm of nigh-bullets.
A Cold War situation is highly probable as a result of their creation, yes. Go to Comment
That was the chief inspirational effect, yes. Rather than a sustained and steady operative field, this is a split-second pulse of utter devastation. The Device is a bomb with fallout. The Cannon is just a devastating gun. Go to Comment
When running a new party, get around the question of plot density by having the first discovery to be a deck of fate, or whatever you call it. If you use a real deck, you should definitely stack it to have the desired outcome, which is to curse the party to attract weird things to happen and involve them. This should not be told to the players at the time, so that they won't just up and try to get themselves 'decursed'. Though quite why they would want to is beyond me.