Your suggestion is to add a field that will only be used in a single status, which goes against the simplicity of GH Issues (which this update already makes contentious enough, looking at the comments here).

Also, realistically, there will be a mention of the issue in the final ticket, so is scrolling down to the bottom of the issue that hard? You're making it seem like it'd be buried in the middle of the timeline and while that can happen, I don't see that being anything but an edge case. Most tickets won't be referenced after they're closed as dupes.