It's on HBO, so sponsors aren't really an issue. However, if the show was dependent on sponsors, content and execution would likely be even more critical than it usually is for potential sponsors.
I don't think there is any way we would have seen white people as slaves. Dehumanization was one of the most important excuses used to justify slavery and it was made that much easier because of the difference in looks (and culture) between Black people and White people. Since other minorities came to the country voluntarily, as opposed to being kidnapped as were most Black people, I don't think any would have been slaves in the same way.
I agree that white people wouldn't become slaves but at the same time I feel like those at the top would still want to create a divide between the rich and the poor. I'm curious as to how they would use slavery to do that. Wouldn't poor white people be complaining about how their is no jobs because they are being filled by slave labor?. I just had a thought but what if this world had things that liberals usually see as good things like a mandatory wage,free health care etc, but it has been perverted to help keep any kind of public outcry over slavery from ever going beyond the ethical reasons to end slavery.
Jason