Problem is if this were to go into place it would be a huge rallying cry against future tax cuts (and even more so against tax irradication) until the grace period is over. Anytime during this grace period when taxes gets lowered would be effectively lowering the value of the reperations, lowering our concept of guilt over slavery. This could turn into the ultimate weapon against tax cuts.
Then there's still the problem with how many blacks live below the poverty line (more than any other minority), none of them will gain any benefit from this because they already don't pay taxes. It's easily argued that these are the people owed the most (because they've had such a hard time oercoming the "obstacles" of slavery) and they wouldn't benefit at all.
All around a bad plan that doesn't do an adequate job of addressing the heart of the reperations argument or offer any tool to use against our abusive tax system.
The problem with your argument is the presumption that without these kind of bold action we will ever see any of the tax eradication that you're talking about.
Just think how difficult a time, with a republican president, and republican controlled house and senate, we had in getting any kind of tax cut through. I simply do not see any significant tax cuts on the horizon,barring something that will shake the current system up in a major way. I think that's why there is the discussion of the sales tax.
Bottomline, am I convinced this idea by Keyes will work, not yet. But I do think it's a very interesting idea with a lot of potential, and I applaud him for presenting it so we can discuss it, rather than strike him down because we have knee jerk negative reaction to a slogans like "reparations".