This is an old question, but the gist would be applicable to other specific requests.
In general, tags serve certain purposes. Mainly, they attract the appropriate people to answer the question and serve as common search terms for people with a similar requirement. Tags can also add important context to limit or focus the question.
The subject of accessibility involves specialized knowledge that isn't within the purview of the site. So it wouldn't be on-topic to ask a question where you're looking for site members to bring that expertise (even if, by coincidence, some members might have the relevant knowledge). However, that doesn't mean nothing about the project would be on-topic here.
Someone with specialized knowledge could help describe ideas, objectives, and requirements for projects that would be helpful for people with specific needs. That part of things isn't within the scope of the site.
But that could lead to a project based on those conceptual efforts. If all of the requirements can be met with the usual methods and materials, there wouldn't need to be a question here. But if meeting those requirements presented a specific challenge, how to accomplish the results might be a good question for the site. In that case, the tags would relate to the project and the issues to be solved here. Why the project came to exist can add some interesting context to the body of the question, but isn't relevant for tagging.