I think in many cases (and in the linked example) too many subquestions means that what is being requested is a tutorial, rather than an answer. Requests for existing off site resources, including tutorials, are off topic. I see no reason to treat requests to write new tutorials any differently.
The Q&A format works well because questions are specific, which makes answers comparable. This means that asking a computer graphics question not only gets you a variety of expert answers, but also meaningful expert voting, to highlight the most useful answer. The larger the number of subquestions that are squeezed into a question post, the wider will be the variety of answers that are worthy of upvotes. This means that votes from an expert community no longer distinguish the best answers, making the question nearer to a forum thread or a blog. Forums and blogs serve a different purpose, and allowing them here sacrifices the benefits of expert voting.
I'm deliberately focusing on the need to recognise tutorial questions as off topic, rather than on what to do with a question after it is closed.
Anyone is free to post new questions, and questions will be judged on their merit, rather than whether their inspiration came from a real world problem or a subsection of a previous closed question.
What is important to make this site useful is a community of experts who are prepared to downvote and vote to close, to keep the body of questions relevant and specific. Provided we maintain this, questions will continue to come in and the site and the community will both continue to grow. There is no need to worry about a question that is closed and not edited.
We can be friendly and helpful when putting questions on hold, and encourage editing to allow reopening, but for those question authors who choose not to edit, letting the question stay closed is a natural part of how a Q&A site works.
Everyone should feel free to suggest improvements to closed questions, or to ask new related questions that better fit the site. However, please do not see this as a requirement. Having closed questions is not a bad sign - in fact I see it as a sign of good health of the site. It means we are being discerning and are not desperate for questions.