It must be remembered that black soldiery was contemplated only at the last ditch by Confederate leaders. Some will rightly point out that some blacks DID support the South and some served willingly in the ranks; but this should not be read as a more enlightened view by the Confederate leadership on the slavery question than in fact existed.
Cleburne's career was, by all accounts, done considerable damage by his proposal. However much Lee might have sympathized with the suggestion, he deprecated the divisions such a policy would entail. And as you rightly point out, most of the rest of the high command of the Army of Tennessee opposed the proposal. The CSA only authorized black soldiers in March 1865 as the South reached the final stages of disintegration.
To suggest that all of this was a signpost for the change in attitudes towards slavery, as Monterrosa and others do, seems to me unsustainable. What little the CSA did was done only under extreme duress, as a last ditch measure with most of the South overrun and the white manpower pool bled utterly dry.
Would slavery have come to an end eventually in the South? almost certainly.
But it lasted another full generation in Brazil and Cuba. Given that it was in healthier shape in the South than in either of those nations, it's hard to think it would not have lasted at least that long in a free CSA. My own guessis that it would have lasted, sans external pressure or force, until the early 20th century, gradually phased out in some compensated scheme.
Turtledove in his books suggests the likeliest scenario: a CSA forced to emancipate slaves legally (though hardly better in reality to a grim sharecroppery) under pressure from its Anglo-French allies the next time it faced war with a rump United States.
If memory serves President Longstreet freed the slaves by presidential decree, in complete violation of the confederate constitution. But then Turtledove's knowledge of the U.S. Constitution isn't much better. I believe that the Socialist New York Congresswoman wins her seat by beating a Democrat who had been appointed to fill the vacant seat, again in violation of the Constitution.
the first CSA "ALL-BLACK" units were formed in early 1861.
check out the LA Native Guards (who were FORCED in 1862 to fight for the union OR be sold INTO slavery!), the Mississippi Ethopian Free Rifles, The GA Sables & other all-black,Latino/black & mixed Indian/black units (like the SEMINOLE RIFLES for example, which was about 50% blacks. fyi, there were 2 white guys in that unit, as well.).
according to Dr H R Blackerby by mid-1862 the CSA military forces were DESEGREGATED down to company level. the damnyankees NEVER desegregated their military forces, period.
the CSA also had SEVERAL black commissioned officers;the damnyankees had NONE!
free dixie,sw