All I can say is "meh", I'd have to learn more about it to know if I wanted to play it. Truthfully the slave trade in the era your talking about would have very little in the way of gamability. The actual reality is simply loading up on goods in Europe, sailing off to The Middle East, buying captured blacks from Arabs with the goods, and then sailing the slaves back to the Americas or back to Europe (depending on the trader and the time period). It would just be another trading sim, and other than perhaps fighting pirates occasionally or something there wouldn't be a lot to do. All the crap you hear about whites landing in raiding parties and dragging off screaming black people to be slaves is complete crap, the blacks were largely enslaved by arabs or other blacks and then sold, and this game saying "buy slaves" seems to at least have this right.
Now it could be more interesting if they set the game in another time period. See, whites didn't practice slavery very long, we just tend to tolerate the whining and feel guilty as despite all criticisms we're the most moral people in the world if you want to draw things along racial lines. Whites were never great slavers, rather our actual mark on human history is that we ENDED slavery which had been practiced by people of other ethnicities when they dominated. Blacks in the fertile crescent region, dusky and olive skinned mediterreneans, arabs, and others were the ones who practiced slavery for thousands of years. What's more it's kind of ridiculous when you look at the actual history of slavery and have the occasional people screaming about white cultural superiority as a natural order or whatever, because while we dominate now (and have for a while) in reality "we" (whites) were the planet's "special kids" and late bloomers. While we developed better than anyone in the long term and dominate globally for the moment, throughout most of human history we were actually the guys leaping around in crude skins and living in caves and crude dwellings while everyone else built these great civilizations. Babylon, Persia, Egypt, and of couse Greece and Rome all had these massive civilizations, and the white barbarians were hunted, murdered, and enslaved as a "lesser race", "we" didn't really get started on any signifigant level until after the fall of Rome.
Now, if I was going to want to play a game based around a slavery simulation I'd want to play such a game set in the ancient world during the actual golden age of slavery. That is where you'd have to outfit your raiding parties, engage in skirmish warfare to capture people, and then work on breaking and training slaves for differant purposes. As you begin you'd probably want to raid and sell newly captured slaves to others, but as you develop your empire you'd probably want to break and train the slaves so you could sell skilled and broken slaves to other businesses. As time went on you might very well start running your own whorehouses, gladiator stables, and hiring your slaves out for construction and such.
In the TV series Spartacus the gladiator school was not capturing it's own slaves, but you can see the potential for politics you might get involved in there.
Of course such a game wouldn't be politically correct as it would shatter the illusion of "blacks are victims, whites are evil", while at the same time not being intentionally baiting backlash for attention which is what the developers here seem to want. I very much doubt this game is being developed purely as an entertainment product as much as "for the lulz", with similar mentality behind it to games like "Ethnic Cleansing" or various conencetration camp and school massacre simulations.
That said, a really good ancient world slaving simulation full of sex, violence, decadent depravity, politics, and of course violence would be pretty awesome. It could include both empire management elements, and RPG development of your protaganist and his various troops used for raiding. Ultimatly I think it would work best set up sort of like "Mount and Blade" which already has a system for taking prisoners alive.