Was abolition or emancipation of slaves ever considered on a wide scale in the Roman Empire?

This is a very interesting question for which I don't have a direct answer, but I can offer a secondary source on the frequency of emancipation in the Roman Empire. In her new history of Ancient Rome, SPQR, Mary Beard offers the following:

Roman slavery was in some respects as brutal as Roman methods of military conquest. But for many Roman slaves, particularly those working in urban domestic contexts rather than toiling in the fields or mines, it was not necessarily a life sentence. They were regularly given their freedom, or they bought it with cash they had managed to save up; and if their owner was a Roman citizen, then they also gained full Roman citizenship, with almost no disadvantages as against those who were freeborn.... The practice of emancipation - or manumission, to follow the Latin term - was such a distinctive feature of Roman culture that outsiders at the time remarked upon it and saw it as a powerful factor in Rome's success. As one king of Macedon observed in the third century BCE, it was in this way that 'the Romans have enlarged their country'. The scale was so great that some historians reckon that, by the second century CE, the majority of the free citizen population of the city of Rome had slaves somewhere in their ancestry.

I'm sorry that this doesn't directly answer your question. I'm not an expert on the topic, but I'd just read this a few days ago and thought it might interest you.

Source: Mary Beard, SPQR, 68.