I think the most likely outcome is that the bill would be presented, generally admitted to be a just account, and then White Americans would overwhelmingly refuse to pay it. So things would not get as far as the lawyers and bureaucrats. What the outcome of the refusal would be, I don't know, but I do think the bill should be itemized, added up and presented so we all know what it is -- at least, as long as the United States persists in liberal anti-egalitarianism, the worship of private wealth, and pseudo-individualism. The bill could hang out in the political background, reminding us all that the vaunted works of the White Man are solidly based on theft and murder. _We_ know that, but a lot of people are surprised to hear it.
But assuming that there were some chance of reparations, note that we are not talking about a government tit here if we adhere strictly to the notion of a money payment to specific persons. If by some miracle the bill were paid, it would be a transfer of wealth, potentially capital, not of dubious entitlements to be paid at the ruling class's pleasure at some point in the future, e.g. Welfare, Social Security. I think that's an important point. Otherwise the payment would be nothing more than a bit of mummery between segments of the bourgeoisie. This is owed money, and it can be construed as owed in specific amounts to identifiable persons, most of whom, being poor or working-class, would find their lives radically changed as a result of payment. If by contrast the payment is construed as owed to a group or category, most of it will be stolen by manipulators -- see the concurrent discussion about the diversion of moneys paid as reparations for the Holocaust.
Reparations are a liberal game, and it is best to play the game as closely to the basic rules as possible to get a good liberal result. It does not have much to do with getting rid of racism, although the receipt of $200,000 a head by a minority would certainly change their social status, if only temporarily, in a society which respects wealth as much as the U.S. does. I think if you want to attack racism seriously, you have to think about removing the fundamental note of class war which racism resonates, and this is a much more serious undertaking than paying off the slavery debt while everything else remains the same.
But those who want to keep liberalism and capitalism should certainly be told to pay up.