I guess asking to create a package in a question would "need more focus", i.e., is too broad for the site. Converting an answer to a specific question into a generally applicable package is likely to be a lot of work, in providing sensible user commands, testing, writing documentation, and further maintainance.
Alternatively it could be argued that such a question is focused - writing a package is a lot of work but answering a question about writing a package can be quick (yes or no, possibly with some arguments in case of 'no'). However, in this case it is likely to be opinion-based, because the answer is "this is/is not a good idea because X". Also the voting on such a question would be problematic, it could be interpreted as a meta-style "upvote=support the request, downvote=disagree with the request", which means you could loose reputation not because the question is bad but because people disagree with you that a package should be created. Asking such a question on Meta itself is also not a good fit because Meta questions should be about the site only.
Both of the above arguments are reason for closure of such a question. Creating a tag therefore does not seem to be a good idea.
You could leave a comment under the answer to suggest the idea to the answerer. If they are interested then such a comment will be sufficient to initiate the process. Converting answers into packages has happened 73 times to date, see Which questions led to the creation of a new package?.
package-writing
to cover that, I'd say.) ... – moewe Jan 4 at 7:42.sty
(plus the things others have already mentioned). I'd want that package to be easier customizable than an answer on TeX.SX, so I'd have to add options and generalise the code, etc. – Skillmon Jan 5 at 15:36