Yeah, sorry about that; I had lost inspiration and interest. I might continue it if I feel like it (what's the cut-off for thread necromancy?), but probably not.
As for the actual feasibility of a "Mormon Empire", completely ASB. And I say this as a Mormon. We had a good-sized empire/area of influence in OTL, and even if the population of the Church is helped by less splintering, and more of a martial tradition (as I was going to have happen in my TL), it's basically impossible for them to have an "empire" beyond their influence OTL. The only way for them to survive as a nation is to have the US avoid fighting Mexico, and thus taking the west. And even then, the Mormons have to be incredibly lucky.
An interesting idea however, would be Mormons heading South instead of West, and ending up on one of the Caribbean islands. I might write that. Hmm...
I'd talk more about how the Mormons having a martial tradition, and the "fever dream" thing is stupid, but I don't really want to get into an argument.
On a side note, before I begin my main point, I too would love to see you continue your original TL; it sounded interesting, and I'd love to learn more about LDS History.
Now, one to the main point. So, lets say that the US avoids a war with Mexico. It wouldn't be too difficult; have Henry Clay defeat Polk and finally get his chance to shine. Clay would have been hostile to any outisde conflict that took away from his domestic plan.
So we have the large Mormon exodus to the Great Salt Lake and surrounding environs. Their population begins to grow and the Mexican government takes a dislike to these strange Anglo-freebooters who refuse to accept the authority of Mexico City.
Lets say that war finally breaks out in the 1860s. The US, without the Mexican-American War, may or may not be in a Civil War by this point. If not, volunteers from the US begin to drift into the region; they view the Mormans as plucky rebels against the hated Mexican government. Texas redux, if you will. The fact that the Mormons got chased from the US is overlooked by many (although not all.)
The Mormons pull out a victory, and the state of Deseret is established, including OTL Utah, as well as Arizona and New Mexico. The US doesn't really care, as it doesn't want these territories in the first place. It may start looking at California; but i could see, with the Gold Rush, the Mormon Revolt occuring at the same time as an Anglo rebellion in California.
Basically, you end up with a rather large, but underpopulated, Deseret. Not an empire by any stretch of the imagination, but a unified and indepdent state.