Comics don't have a good track record in making gender pallet-swap heroes.
Wonder Woman's weird power-creep into becoming an ersatz superman made her publication, television and film history pretty abysmal and/or highly contentious from 1980 until (ironically) Brian Azzarello picked it up for New 52 and has done a great job of winning fans of all kinds.
X-23 was not well received at first by Marvel fanboys, and honestly, why would they? Her origin story was not at all endearing as an introduction to a character. She's grown a bit since then in the hands of better writers, but this was not always the case.
Then there are counter-parts. The non-replacements who just muck-up the universe. See "Super Girl" who had to be made Kryptonian and then had to be made Superman's family so that she wouldn't replace Lois as a love interest (because it's totally likely that his older cousin would also survive and also make it to earth, but not someone on the other side of the planet). Or Kate Kane, Batwoman who it turns out is part of a family every bit as old and storied as the Waynes, which everyone has known about all this time... except the audience? Again, fucking terribly writing.
Lately there has been reversal in this and I'm thrilled to see it. Fans are apparently loving Spider Gwen. And I will give Jason Aaron every benefit of the doubt on Thor, given the man wrote the spectacular Weapon X, Scalped, Southern Bastards... I could go on.
But every time someone says "we're going to take a mantle you love and replace the actor in it" I'm reminded of all the times this has been fucked up before and I ask "why?"
Too often it's not compelling. Too often in the past these new characters have had to cling to their male counter-parts, which is an insult to everyone (character included). Too often this is done without thinking of the ramifications for the history of the character (Batwoman) or the future of the character (Wonder Woman).
It's also an insult because it leaves perfectly good character with huge promises sitting on the editor's pile. This isn't a matter of "you have your toys, we have ours" but rather that there are agents worthy of narrative use who will just keep taking a back burner.
How long has it taken to get another good Storm story? Why Jean Grey just permanently awful? Why the hell did they make Jubilee a vampire?!
As a comic fan it frustrates me because it seems like the wrong solution to the problem.
As for the anger regarding "just make a new character"... yea, comics need new characters. They need them desperately. Of the comics I'm actively reading, only one is a legacy title.
The rest are things like Sex Criminals, Black Science, The Wicked + The Divine, and East of West, all of which are chockablock with the sorts of strong, enigmatic and compelling characters you don't get in old titles.