There is part of me that want a consistency in people's outrage. If race bending characters in A:TLA is bad then all race bending is bad. But part of that outcry is actually about employment opportunities for Asian or native American actors.
For the new FF I CAN accept a black Johnny since they made Dr Franklin Richards black (they are doing the Ultimate origin story). And since we live in a time of extended families and interracial marriage is more and more common, his sister being white would cause about a two second pause before I adjust and accept if it was a real life situation. Only question I would have is whether Johnny is a half-brother, step-brother or Sue was adopted but in the end it really doesn't matter to the characters of Johnny and Sue. As long as they grew up together long enough the family dynamic between them will be there.
The problem with the FF casting was that Johnny was the first announced with zero other info about what they were doing. And needless to say it freaked out the fanbase, more so than a black Spider-man would. It's less of a problem now that I've seen the full trailer and I have an inkling what they are doing. It's like that undying rumor that Doom is an angry blogger. Doom is in the trailer and like Ultimate FF is working on the project along with the other four, goes along with them and is equally affected. And recently there was a rumor that the reshoots for the movie (all movies have reshoots) were directed by someone else because the studio hated the movie and that got shot down.
As I've said about Jimmy Olsen, it's the turning him into a hunk rather than him being black that is more shocking. Lets reflect the demographic of the world we live in and we can do this with the secondary characters. But Jimmy is suppose to be a skinny, average height, somewhat dorky guy, not 6'3" with a 6-pack who could walk into a bar and leave with anyone he wants.

So not the Jimmy I expected.