What is it about this topic that is not already covered by the sites listed above?
Thank you for asking. You will find several detailed example scenarios in my other question here: On why having....
In the meanwhile, I'd like to also answer your question here.
ServerFault and DevOps
So lets start with your statement, that the devops domain is fully included inside serverfault domain. Actually it is not, as several overlappings with other SE sites can be seen, but before I'll get back to this, just think how DevOps focuses exclusively around the SDLC. As many people see production deployment, configuration and support as a later phase of the SDLC iteration, many other even think that's an individual process on its own. The different focus for questions involving the same tools would need different expertise from the users answering it, and more importantly a difference in scope. Additionally, there are release management and build automation phases, that I see overlapping serverfault very slightly, if not at all. And lastly, there is infrastructural code to be written, but that leads to the next:
StackOverflow and DevOps
DevOps is about designing good practices, infrastructures, and implement them; for each, there is configuration, or code, or both, to be written. Most code issues or how-to questions would be redirected to stackoverflow, because that is the natural place to get that kind of answers. But a scope of this kind of questions exists for which stackoverflow is not the right place to ask: it is when asking recommendation or localized questions, not directly involving code, that would be of little help to anybody else in the broader SO community, but that would be very well received in the devops one (be it specifying convention for the build process, or ways of setting up artifact promotion, or laying out scm branching for certain releases processes). The risk is of having some opinionated answers, or too much localized answers, or code/tool recommendations, which while explicitly forbidden on SO, would actually be of big value in here. Additionally, there is a phase when the infrastrcture needs to be designed, decision has to be made about the tools in the pipeline, and the single pieces integrated together. It is a discussion that does not involve anything involving coding or configuration, just context and target. For that, I see as the most relevant stackexchange site to ask, programmers SE, so lets it have its own section:
Programmers and DevOps
In my vision of this DevOps proposal, a big part, if not the vast majority of questions, would involve general discussion about designing infrastructural relations, or whole architectures of systems, in support of the SDLC. It is in my opinion the same scope of questions I see asked on programmers, but within a different context (supporting the SDLC from outside).
Ok, so DevOps has overlappings in many other broader technical areas, in a way that is so horizontal, that the skills made (big enough) companies create new teams with new responsibilities. Because of these peculiarities, new questions can be asked that cannot be covered entirely in any of the overlapping existing site, thus making this proposal a good fit for a stackexchange q&a new site. That said, there is a risk to have questions asked that would only fall in the stackoverflow or serverfault (or others) domain: in those cases, they would be closed or migrated, as happened already with many sample questions in the proposal.
A useful parallel may be to look at security.SE. Are there security questions on SO? Yes. Are there security questions on SF? Yes. But security.SE provides a home for questions that don't fit nicely on either of those sites, and tends to cover a lot of higher-level process-oriented questions that aren't on-topic elsewhere. I could see a DevOps SE being similar.
Questions on culture, process and organizational structure are not covered by the other sites. Large part of DevOps are the theories like systems thinking, theory of constraints, theory of scientific revolutions, six sigma, lean and frameworks like Kanban, Kaizen and Cynefin. The change in culture at organizations, study of change itself. Paradigm shifts, pivots and innovation accounting for example are also hardly ever discussed by the mentioned StackExchanges.
DevOps overlap on ServerFault is minor.
Server deployment methodology to handle things like QA, test and development environments.
Server management for software development environments
Operational process mechanisms for creation and tear down of various servers required during an SDLC
Sizing compute, storage and network for deployment of applications
This is a relatively minor overlap into ServerFault and realistically, those types of questions relating to above should probably me migrated to ServerFault if they popped up.
I can't server infrastructure resources (humans) flowing to a DevOps SE site to ask infrastructure questions even though SDLC resources might be asking them.