How does it sound to you natives to make a contraction like this:
No, you mayn't. (= may not)
Sounds like a generalization from other forms like shan't
. So dialectal at best (I don't know if anyone actually says this though).
There is another thing I wonder. Would a regular anglophone understand this:
What does it be? (= 'What is it', expressed with do-support as English use to use to construct questions)
This sounds unnatural. Semantically, it's like you're implying the subject is ever anything else, and inquiring what is it at the present time. So totally different implications from "what is it?", not to mention it just sounds unnatural.
How does it sound to you if one doesn't make do-support at verbs that usually have them when asking questions? Is it understandable for a regular anglophone? For example:
Understand you? (= Do you understand)
What play you? (= What do you play)
Sounds like Yoda talking, this does!
Nb: "You understand?" is perfectly acceptable.