Introducing relationships between issues will considerably increase the complexity of GitLab. That is not a reason not to do it. But it is a reason for us to be strategic in when we do it, and ensure we have a good design that is scalable and aligns with our other initiatives.

Now let me ask you, do you write JS for a single page application differently from a "traditional" web application? I sure hope you do! In a "traditional" application, you can get away with being sloppy because every time the user navigates to a new page, their browser destroys the DOM and the JavaScript context. SPAs, though, require a more thoughtful approach.