What's the difference?
PhysicalFitness.SE is within the scope of the category Biology.SE, but is separated, because people on physical fitness wish to apply human biology to practical matters of improving their own bodies, where as people on biology are interested in human biology for the sake of science. Similarly, people on Mind are interested in improving mental fitness and the subjectivity and their individual use of their mind, rather than general scientific principles about minds.
Most all of the questions (and all of the SE quality questions) of this proposal can be asked on cogsci. Some already even have answers on cogsci. The migrations between the two sites would be impossible to determine.
The field of Cognitive Science generally covers a very, very broad range of topics, including artificial intelligence, linguistics, anthropology, neural networking, and philosophy. These are not the goals of this proposed site, which is designed to focus more specifically on the science and practice of psychology as it relates to improving mental fitness and experience of life. I would say that this site is designed to be more practically focused.
I would compare them to Code Review, Stack Overflow, and Code Golf; the topics may overlap, but the questions and answers are specific to a manner of interacting with the topic. It seems to me this proposal is geared toward practical personal application; something like a "this is a problem I face, does anybody have advice" whereas the impression Cognitive Sciences gives off (whether intended or not) seems much more geared toward academic purposes.
Under-20-word proposal descriptions aside, Cognitive Sciences appears more specific to social/cognitive science students, professionals and researchers, whilst the impression I get from Mind is one for those more directly impacted or less academic (like a place where a layman can seek professional advice and the opinions/experiences of other laypeople). I see great value of a well-educated community with knowledgeable moderation, strong habits of source referencing and other academic necessities, but I'm concerned that mixing the academically purposed site with one focused on practical implementation may:
- Distract from ongoing academic/scientific discourse when uninformed users become part of the same community.
- Appear to be more for that purpose or otherwise put-off visitors without the academic background to understand answers regarding the broader science
An argument can be made that all people trying to learn fall into the category of students, but it's worth noting that moderation between these two approaches may require different policies.
It may also be meaningful to consider the types of users who might seek advice concerning mental conditions. Perhaps unavoidable to some extent, but I imagine someone with esteem and depression issues looking for the advice and sense of belonging/similarity to others with mental illness. So he happens upon a Q&A site via search and jumps in to a question about why someone always feels anxious about group environments and what she can do to mitigate it (thinking "I know just what you mean!") only to stumble on highly voted answers to PhD theses and negative votes on a person's personal coping technique. If the new gentleman successfully uses the same coping technique described in the personal answer and sees that "society" considers his approach to be "stupid" then I don't think the site will be able to serve his needs.