Beating Trump is not going to be easy. Implementing big programs that actually have a lot of support like some sort of GND, some sort of Medicare-for-all and some sort of universal child care program will not be easy, even if the Democrats do prevail. It therefore follows that Democrats should avoid pushing unpopular programs that will meet with stiff resistance and undermine their electoral and governance chances.
Such a program is reparations for the descendants of slaves. Whatever one's views on the moral justification for such a program (or its workability), it should not be controversial that such a program is likely to be massively unpopular (see below). Polling data indicate that even among black voters such an idea is not hugely popular, among Hispanics is not popular at all and among whites it is very unpopular indeed. This does not seem like a wise approach to building a winning coalition for 2020.
Oddly, we know have several candidates for the Democratic Presidential nomination who are going on record as in some way backing this idea. Even though these commitments in most cases are quite vague, it is not clear how easy it will be to keep those commitments vague or to drop them at a future date. Presumably all of this has a great deal to do with Democratic primary politics. But that does not mean it will not come back to bite whoever the nominee is in the general. I suggest all potential Democratic nominees take this possibility seriously. Four more years of Donald Trump should concentrate the mind.