I’m not on Twitter so haven’t seen if anything was there, but my GoogleFu hasn’t give me anything specifically for a racism archive tag. I have seen a few folks raise the issue that if we add a racism warning they would also like to see an incest warning, which works for me, though users do seem to tag relationship and incest pretty well in my experience (so someone could still filter those works from their fandoms).

Things I have found:
-A rather lip-service link round up from OTW about racism and activism
-A petition for a block button

I look forward to everything being posted on fandomgiftbox so that I can see whether I'm able to make any gifts!