Mandatory deportation AND billing the Northern states for the costs.
I think it's fair to say that even in 1860, most people could not imagine former slaves living peacefully with their former slave-masters.
I think from Lincoln's standpoint viz-a-viz colonization was that blacks in the U.S. faced a future where they were not considered citizens and where the legal discrimination and lack of rights that they endured in the North was even more prevalent in the South. And end to slavery would just make things worse. Why not assist blacks in carving out their own life free from the burdens placed on them in the U.S.? Where they could run their own show? And where really was he wrong?
Ha! Oh, that Jeffy-boy, what a comedian he was.
But even so, his slave-holder buddies would have none of such a plan, then or any time later.