If we limit ourselves to people promoting the A+ brand, then the answer is that the brand didn't catch on for various reasons, not least of which are the screaming caps lock of rage on the forums.
If we consider A+ more broadly as the acceptance of ideas from the online social justice memesphere into the freethought community, then I would say that "Atheism Plus" has been doing fairly well. Skepticon cut off CFI sponsorship, for example, because CFI was considered insufficiently pure. At least a half dozen prominent secular leaders have been accused of sexism or sexual assault. At this point, you'd be hard pressed to name a prominent national American freethought organization that hasn't been accused of oppression by someone writing at FtB or Patheos. The promotion of social justice callout culture proceeds apace, regardless of the A+ branding.
Sure, but what effect has that had? Being called out on an Internet forum happens to a lot of groups and people, but it doesn't always mean much. Has CFI, for instance, suffered in some noticeable way due to the Skepticon boycot and other criticism? Have they lost members, significant funds, conference venues? Have their ability to engage in activism and outreach been impacted? Or is it just a bunch of people yelling on forums and blogs and not affecting anything? Based on what I've seen, it's by and large the latter.
As for A+'s decline and the reasons thereof, in addition to being ineffective in terms of outreach due to the razor-lined hugbox nature of the forum ("we will all love each other and agree with each other! And if you don't we will INCINERATE you!") is that many of the prominent A+ people have themselves been castigated by the feminist groups they are trying to appeal to, so they're getting hammered on both sides. This was presaged early on when Natalie Reed, in her blogpost about leaving FTB and the atheist movement, implied that A+ didn't go far enough for her. Later, PZ Myers reached out to Shakesville's Melissa McEwan by republishing her list of things atheists could do to be more appealing to feminist groups. But, in response, she (as well as her biggest-name moderator, Ana Mardoll) proceeded to excoriate him on their blogs because he made a small change of wording from her posts (she said something like, "these are rules all men should follow," and he changed that to "rules all humans should follow" or something like that). Richard Carrier, the 'intellectual artillery' of A+, has been slammed on Mardoll's and McEwan's blogs for being a rape apologist. If the A+ people are categorized as enemies by these groups even after all they've done, people will wonder what the point is. A+ demands all this from you, and then it doesn't even help makes the allies they wanted to make... so why bother?
This gets back to something Greta Christina was saying, I think. She made the tactical argument that A+ is worthwhile even if it dilutes the resources of atheist activists because it's a way for atheists to get new people onboard; folks who don't really care about prayer in schools or Creationism might still take up those issues if we in turn take up social justice issues they do care about. The net result will be, she argued, that we'll have more resources for atheist activism than before, since the gains from the new people offset what we divert to other issues. But even setting aside the implied assumption that atheist activism is by default a straight white male thing and that we have to directly pander to members of other groups to get them to care about it (which, honestly, I find offensive in and of itself), it misses that a lot of the groups A+ wants to work with are not open to this kind of compromise. They aren't in support of an arrangement where A+ helps them with something and then they help A+ with something, where different activist groups who care about different things can meet and pool resources and team up to better all. They want to accomplish their own causes, enforce their own standards, etc, and no attempts by A+ to meet them halfway will be enough.
This is why the alliances A+ is proposing don't work and cannot work -- because it's always shown as one-sided, with atheists working on other SJ causes and adopting their standards, rather than the reverse. We've seen a lot of efforts to remove sexism, racism, etc from the atheist community -- but have any of these groups looked at efforts to remove superstition and irrationality from the feminist and anti-racist communities? Shouldn't that be just as important? We've seen how A+ insists that atheists adopt the standards of other SJ communities (you can use whatever tone you want when responding to something that offends you, you can't argue with someone's personal experience or the conclusions they drew from it, what you're allowed to say depends on your identity, etc), but they don't ever seem to argue that the other SJ activists should adopt atheism standards. As a more concrete example, we've seen McEwan's big list of things atheist groups must do to be a welcoming place to feminists. She's written nothing about what feminist groups must do to welcome atheists, and as far as I can tell, neither have any other big names. Atheists aligning with these groups must sacrifice a lot, even their skepticism when it comes to the policies of these groups. After all, we've all seen what happens when an atheist argues that a moderation decision was made irrationally, or that a word shouldn't be on the banned-terms list (e.g., 'stupid') -- they get castigated and banned. But none of the other SJ activists seem willing to give up anything to make things equally 'safe' for atheists.
I think a large part of this is the idea that atheist activism isn't a 'real' SJ cause, and that being an atheist isn't a 'real' oppression. The A+ people like to talk about how traditional skeptics, all old privileged white men, do nothing but kick back and laugh at idiots who believe in Bigfoot or the Eucharist. Meanwhile it's only them (A+ people) who care about making the world a better place. Even when they refer to our activism, it's usually a derogatory comment about "bravely making sure the world is safe from nativity scenes in public parks!" And by that logic, diverting atheist resources to fighting for other causes redirects them from something useless ("laughing at idiots") to something important ("fighting discrimination"). They either don't know or don't care about the importance of our activism, and so they argue we should just devote our time and resources to fighting for them instead.
Problem is, atheist activism and skeptical outreach is actually really important. We fight Creationism and ensure that students can learn about biology. We oppose the charlatans and con-artists who use woo and pseudoscience to defraud those who are grieving, or naive, or otherwise vulnerable. We seek to expose the crimes of those who abuse the power of their pulpits to commit crimes and hide behind religious texts to divert suspicion. We help those like Jessica Alquist who are horribly demonized by religious communities. We argue against the harmful religious beliefs that sex is shameful, that humans should believe they are inherently depraved, that gay people deserve damnation, and so forth. And, yes, we do oppose nativity scenes and so forth, because it is in fact a problem when a city erects something supporting a particular religion. This work is, in fact, important. It's just as important as the other causes of the other Social Justice groups. And so the arguments that we should stop doing what we're doing and devote ourselves entirely to other groups, because it's not like we were doing anything important anyway... all they reveal is a complete lack of understanding or respect on the speaker's part as to what atheist activism actually is.
Atheist activism is important. The atheists A+ is arguing with know this. And when the A+ group tells us that we should accept the standards of other SJ sites but never insist on our own, that we should take on their causes, spend less time and attention on ours, and then maybe someday we can get back to what we're doing... they are only further marginalizing themselves.
