Isabel Schechter tweeted a comment by N. K. Jemisin from a Wiscon panel —
A rhetorical question, naturally. Of just the kind fans can’t resist answering.
There are a number of time travel stories featuring black characters – however, nearly all of them revolve around exactly the dangers Jemisin has in mind. The most famous of these is Octavia Butler’s Kindred.
The authors usually want to explore racism and slavery and pick a historical setting to trigger that issue.
In a few other cases, an author has sent a black protagonist back to a time where the assumptions are more favorable —
Averted in S.M. Stirling’s Nantucket series: Capt. Alston, an African-American Coast Guard officer, is assumed, by the Bronze Age people she encounters, to be a respected Nubian warrior chief. Of course, many presume she is a man until convinced otherwise.