I've read plenty of specs over the years. Some by people I wish had taken the time to ask a simple question like this. Do we really want the next generation to be completely dependent on tools like Microsoft Visio?
Questions about diagrams IMHO can be on-topic if the specific focus of the question is how to use diagrams for things like
a software concept, or
documenting software or software architecture
For example, a question like how can I draw round corners is not specific for software development, a question like is there a consensus to use round corners for the "Foo" elements in the UML diagram type "Bar" to express semantics XYZ could be on-topic.
In my point of view, the question in stake is more of the former type than of the latter (but YMMV), so I think it should stay closed.
Since the OP mentioned it in his "answer" here: a question like "I try to design a domain specific language for unit testing using ASCII art, but I have trouble with the semantics (or unambiguity) for this and that reason" could have been on-topic. Just asking how to improve the look for ASCII art, however, not.
I don't see how this relates to our scope of "professionals, academics, and students working within the systems development life cycle". Yes, we create diagrams , but creating shapes in plain text formats is not unique to software development. You could argue that this is about how to use a text editor to create a diagram rather than the process of creating or maintaining a diagram. You could also argue that it's more about art or design than the diagram. I don't see how you could argue that this is about methods and practices, requirements, architecture, design, quality assurance, testing, configuration management, build, release, or deployment.
Can you make a case as to why this question fits into our scope?
Programmers simply do the most ascii art by far. And in fact, I will use the answer for writing a new unit test domain specific language.
What would be a suitable SE place to ask this question?