How would this affect the world - especially the Union - today? This was the original plan for the State of Deseret.
It may have touched off a Mexican War, giving Mormons a chance to fight for their new homeland and in their fervor give the Mormon Battalion a really good name.
Acceptance this early implies acceptance of polygamy as well. This would really chafe some Easterners and keep the LDS church inside the Corridor.
And some really popular territory in southern California is there too - if I'm not mistaken the city centers of Los Angeles and San Diego lie in Mormon country.