The idea is that the revolutionaries were the voiceless immigrants in the 1770's, the way that people of color are largely voiceless in the 21st Century (and were more so in the 1770's). So really, until the US actually achieves a society where people of color really are equally represented in white-controlled media, Hamilton's casting stipulations probably will not, and should not, change.
As for Angelica always being black, or Eliza always being Asian, or Hamilton always being Latin – I'd say really as long as it's non-white, the characters can really be played by any person of color. Leslie Odom Jr. did recently say he'd want to see the first Asian-American Aaron Burr.
I did have a thought that this'd be great to have some more rappers take part in the show. Chance the Rapper, for one, could do a great job with Aaron Burr.