What if the Nat Turner rebellion in the early 1830s---or something like it--had been in Maryland, not Virginia? (It is true that such slave rebellions were most likely to occur in places where the slaves heavily outnumbered the whites, such as Turner's Southampton County, Virginia. However, there were areas of Maryland with a slave majority, though even Prince George's and Charles Counties did not have as heavy a majority of slaves as Southampton.)
Given that--in general--the lower the percentage of slaves in a state's population, the more likely it was to seriously consider emancipation, and given that Maryland had a lower percentage of slaves than Virginia, might Maryland have been more likely than Virginia to abolish slavery under such circumstances? In OTL the Nat Turner revolt did lead to a reconsideration of slavery in Maryland as well as Virginia. However, because slaveholding southern Maryland had a disproportionate number of seats in the legislature (compared to northern Maryland where blacks were fewer and a higher percentage of them were free), in the end not much was done except for some appropriations for (voluntary) African colonization. Is it possible that if the rebellion had been in their own state, Marylanders--even some southern Marylanders--would come out in favor of a plan for gradual emancipation (combined with mandatory colonization of the newly freed blacks)?