Never.
They'll miss their window unfortunately, because the census data shows that in the next 50 years both Latino and Asian minority bases will explode in size far beyond African American population growth rates (no "11 welfare kids per black mom" jokes, lol, apparantly that stereotype isn't accurate afterall).
Census data also shows that Latinos and Asians report a much higher willingness to vote, and to be involved in politics, than African Americans.
If it doesn't happen in the next 10 years, it never will, and that's not going to happen due to the United States being a few decades away from accepting African-Americans in a leadership posistion. Obama or not, this country is currently ruled by "Nascar Dads", hence why the Republicans keep winning despite the odds being against them, and those good old boys will never vote for some "black sob".