How could it be a revolutionary step if their already tens of thousands of blacks supposedly loyal but unofficial Confederate soldiers? Such a large number surely were not unnoticed by the Confederate government.
There was a difference, in Davis's mind and in fact, between individual blacks (free and slave) serving in the Confederate army and navy in noncombatant roles, and sometimes taking a gun and shooting, and the government deliberately forming fighting units of slaves with the promise of emancipation.
While thousands of blacks certainly served in the Confederate army and navy, most of the time it was in a noncombatant role--for example, driving a supply wagon. Many blacks received Confederate veteran's pensions after the war from the ex-Confederate states (Tennessee gave out pensions to 400+ black veterans), but again, the service was akin to the modern soldier who drives a supply truck.