This may be pie-in-the-sky, but it would be useful if there were some way to connect Meta status-planned tag-cleanup posts to the related tags on the main Super User page.
For example, cleanup of images is discussed in this meta post. The images tag wiki has been edited to warn users not to use the tag, yet I see it being misused on new posts all the time. Moreover, I see questions with this tag being edited but the tag is not replaced by the editor.
Tag wiki excerpts alone are not very effective at altering the tagging behavior of users, and I doubt that anyone follows Meta Super User closely enough to know which tags have been deprecated. There's a pretty clear disconnect here between what's happening on the site and what's being prescribed on Meta.
So what to do? To keep these tags from propagating and to aid the cleanup process, there needs to be a better way to flag users that a deprecated flag is being used. There was a similar meta feature-request for applying a different color scheme to "invalid" tags. While the idea of "invalid" was at issue in the old rejected request, the color flag idea is well suited to this purpose. To be clear, this request is different; it would limit different coloration to tags with status-planned tag-cleanup requests.
My suggestion is that the different coloration only appears when the question is being edited. That is, it only shows up on the edit page, not on the main page or the question page. This is a rough mock-up, but something like this would do:
This would hopefully draw the attention of the question writer or the editor and let them know that a deprecated tag has been used. There may need to be some verbal indication on the page as well to explain the appearance of the tag. Maybe the visual cue alone will lead to the editor mousing over the tag to see the warning in the tag wiki excerpt.
Is this something we're interested in? Is it useful? Can it be done a different, better way?