Does the reuse of Khan bother mostly fans? Odd, because reusing the Joker and giving him different looks never seemed to bother Batman fans or general audiences.
TWOK is thirty years old. "Space Seed" aired in 1967. This movie is aimed at general movie goers who are mostly younger than the age of TWOK, and whose parents may be younger or only a few years older than "Space Seed".
What's more, most in that demographic probably never saw TWOK or especially "Space Seed", and have no idea who Ricardo Montalban was, let alone that he was a Mexican playing an Indian. So what would their hang up with Cumberbatch as Khan be?
For those fans with a hang up, I'd think the star power of Cumberbatch right now will more than compensate for those for whom the movie is now ruined.