It looks like the code for this extension is still being maintained, Have you considered moving it over to Gerrit or Gitlab?
Topic on Extension talk:PageCreator/Flow
It’s funny, I didn’t remember I was written as an author on this extension :) When I did maintenance on it for 1.35 (diff), I noted these magic words were included in Extension:MyVariables. The code for {{PAGECREATOR}} and {{CREATIONTIMESTAMP}} here is exactly the same as for {{FIRSTREVISIONUSER}} and {{FIRSTREVISIONTIMESTAMP}} in MyVariables.
Instead of maintaining one more extension on Gerrit/Gitlab, I think a better alternative is delete this extension and redirect the users to Extension:MyVariables (which is a light extension, not much heavier and more complex extension compared to this one). The only small difficulty for users would be to upgrade the variables: it can be done with Extension:ReplaceText.