In the Topic "Things The Allomantic Metalhead Is No Longer Allowed to Do in the Mistborn Adventure Game" point 90 is "Misthammer 40k is a horrible idea".
I disagree. It is a very fun idea.
In a very alternate future version of the Cosmere everything went to hell just like this.
Part 1: The Crusades of Honor
After Dalinar unified Roshar, locked Odium away somewhere very, very deep in the Cognitive Realm, made peace with the Listeners, he consulted the Knights Radiant and decided to unite the whole Cosmere in one great Nation. In spaceships build by Navani first the Rosharan system was colonized and Ashyn and Braize were "Rosharformed" to inhabitable conditions, complete with their own highstorms and everything. The Listeners wanted no part in the unification process and asked to be settled for themselves on Braize, where they wanted to begin anew, with no interference from all those bothersome shards.
The first other Shardworld encountered outside of the system was Nalthis and after some initial problems the two worlds decided to go together and colonized dozens of other minor shardworlds.
Things started to look worse when Rosharan spaceships encountered their Scadrian counterparts. No one knows who fired the first shot, but in a matter of weeks it did not matter anymore. Shardblades met guns, coinshots and dustbringers blasted each other to the Beyond, lifeless and feruchemists met in day-long battles, the "hemalurgic option" was used on more than one occasion and it went only worse. Fabrials, Class IV awakened objects and Southern-Scadrial-Tec became exponentially more dangerous and at its height the war made desolations look pale by comparison.
Part 2: Meanwhile, on Threnody
At this time, on Threnody most of the population decided that if they had any chance of survival against the shades they needed to change themselves. Armed with knowledge somebody brought from Silverlight they made they transferred their minds to special bodies of metal so they would need neither fire nor blood. Of course, it went wrong. They all became cognitive shadows, trapped in their metallic bodies, and even worse, they became like the shades themselves. And for some reason they decided to enforce the Simple Rules all over the cosmere.
Part 3: The Sel crisis
On Sel, Cosmere-aware individuals decided to reforge all the splintered Shards of the cosmere. Elantrians build power amplifiers that made the original Elantris look pale by comparison, Forgers crafted a giant stamp to forge the shards back together, several scores of Dahkor monks offered to use the energy of their deaths to fuel the ritual, and dozens of other nations chose to participate in one way or another. What could possibly go wrong?
Apparently, quite a lot.
No one knows where the error began, and if somebody realized they were dead before they could do anything. A giant explosion shattered Sel in all three Realms... and that was the least part of the disaster.
The shockwaves shattered and splintered most of the surviving shards at that time and brought the whole Shadesmar into one giant disarray. The surviving Shards were unfortunately Odium (who was locked away deep enough to be not splintered, but freed) and Ruin (who was ironically preserved by the the preservation part of Harmony). Also, in two instances the Ritual worked - Devotion and Ambition were restored to full power. All Shardvessels were killed in the process, and the surviving shards were picked up by some random people.
But it got even worse. Some Splinters of the dead Shards were merged with the survivors, corrupting each other in the process.
A giant perpendicularity of very bad nature replaced the place where Sel was.
Incredibly, there were survivors. By the very Nature of the Dor, the land clung together (along the borders) and was sucked in the cognitive realm. Clever usage of the Dor and technology could save most of the countries, which became giant spaceships.
Part 4: The Crusade of Honor, part II
Scadrial and Roshar/Nalthis decided to agree on a ceasefire for the time being to investigate what had dealt such a blow to the whole Cosmere. They were kind of surprised to find themselves in opposition to four shards which apparently 1) declared war on each other and 2) declared war on all of mankind, and each of the shards had somehow amassed splinters which were several orders of magnitude more dangerous than unbonded spren.
They were further surprised, that many of their own decided to go over to the side of the shards, because "they were the only surviving gods". Dalinar, being tired of this argument, decided to anihilate all Shards to create peace at least on this frontier.
Part 5: The Listener Tragedy
The shockwaves of the Selish Ritual smashed Braize out of the Rosharan system to somewhere far, far away. Together with them went a magnitude of splinters mashed together from an assortment of shards, dead and alive. Several new forms were discovered, and the new forms were apparently there for one reason - war. The skin got green, they got new muscles, brains were somewhat reduced in a sort of trade-off and a very real desire to go to war - everywhere. The other types of Listener were subdued and exploited by the new BigBoss!-Forms, Coooonquest!-Forms and Waaaar!-Forms. With crude spaceships and crude weapons they went to war against the whole cosmere, for no other reason than that it was fun.
Part 6: For the Greater Harmony
A radical element on Scadrial seized the upper hand in the ensuoing chaos. Attacked by the Shards, the Listeners, the Rosharans (although now somewhat more rare) and even the Threnodians on rare occasion the dream of a harmonious future was prevalent, and the Pathists got more and more members. So some pathists decided to create Greater Harmony in the Cosmere - by force. "Harmonists", they called themselves. Their idea was that everybody had a place in the society, and they were to decide it. Scadrian people were forced into guilds named after the 16 basic metals&alloys, ruled by three more guilds, which were named after Atium, Lerasium and Harmononium, with Harmonium always being the most important.
Everybody was judged on their contribution to the Greater Harmony. Protests were eliminated, and the instigators "reeducated".
Part 7: The shism of the Knights Radiant
The four shards knew that Dalinar was the most dangerous foe at the moment - Odium's former vessel had dealt with the Blackthorn before and Odium was not happy with the outcome, so, while he was entangled in the war with the other shards, he also plotted together with them.
They sent visions to Dalinars son, Adolin, who had resurrected his blade and was in command of Edgedancers (Lift did not want to be in charge) and built more and more doubt in his heart. They wispered in Shallan's ear and showed her more and more versions of themselves. They promised knowledge to Jasnah. They drove Kaladin once more to heavy depression. They made Szeth question his duty. Only Renarin they left alone. And so, through a complicated process, they made some of the orders rebell against Urithiru.
Jasnah herself led the rebelling orders - Edgedancers, Elsecallers, Willshapers and Dustbringers. First they went against their loyal comrades inside their orders, then they went in force against Urithiru. Renarin tried to warn his father, but unfortunately too late and the Truthwatchers landed square in the lines of fire and were killed to a man.
Jasnah was killed in the fight by Szeth with nightblood, and was soulcast to stone in turn. Kaladins windrunners were away and came to late and could only try to sort out the aftermath. Adolin, blinded by rage, stuck at his father and wounded him mortally and was in turn killed by his wife, Shallan.
The rest of the Rogue orders fled and hid themselfes somewhere in the cognitive realm.
Kaladin, close to despair, and Shallan, with even more psychological problems, tried to reorganize the remaining orders with relative little sucess. Navani, trying to resurrect her husband, locked him in a life-support-fabrial.
Part 8: Aftermath
Even before Dalinar's semi-death it was complicated to Navigate the cognitive realm. Now, it grew even more complicated. Fortunately, on Nalthis, an Artifact was built which created a clearly visible beacon from Nalthis to Roshar. Unfortunately, it needs about a hundred breaths each day to sustain it. While the number is still comparatively small compared to the population, there are often not enough volunteers to sustain it, and some people need encouragement.
Dalinar's corpse is locked away on the highest level of Urithiru, and no one knows how to resurrect him.
There is war everywhere.
Welcome to Shardhammer 40k.