Downvotes on meta mean disagreement: in this case, with the proposal to introduce the particular tag. Besides being too long (there's 25 character limit), it would not serve the purpose for which tags are introduced: describe what the question is about.
The existence of such meta-tags is problematic, because they allow users to circumvent classifying their question by subject. There are already hundreds of questions on which homework is the only tag. This is despite a warning not to do this, which appears in the homework tag excerpt. The official SE stance is that meta-tags should die. If I had my druthers, homework would die too.
As for providing the source: it can be done at the bottom of question body. SE is unlikely to introduce a special box for this field. Most SE questions are not assigned to the user by someone; they arise in the process of user's work (e.g., programmers working on a company project). Such users would not be willing to disclose what exactly they are doing, which is not a problem as long as they state a clear, self-contained question. A famous recent example is How can I connect to a Tor hidden service using curl in php?