Someone mentioned New Mexico as a possible slave state to counterbalance the loss of DE., but said its population was too small. That didn't stop Nevada from being admitted in 1864, when the whole state was practically empty, admittedly for entirely different reasons. But I can't see the Spanish population of the Santa Fe/Taos area supporting slavery. Perhaps I'm wrong; I have a history of NM somewhere, can't find it right now. I know there was bad blood between these folks and Texans in eastern NM, it just doesn't add up that the Spanish will want to cooperate with the Anglo slaveowners.
So we're too late for Texas to come in as two states, and much too early for the situation to force Kansas to be admitted as a slave state, whether it wants to or not, and in any case, California is coming in, no matter what, so you still need Dred Scott to be decided as it was OTL, plus Delaware is still nominally a slave state, with older slaves in Sussex County, so maybe there is still a balance as it was historically. FWIW, I don't see the Ozarks area becoming an additional state, or the Florida panhandle, either.