Wonderful indeed. Hopefully, this will help you in maintaining your code better without adding too much overhead to your work. The page Quim asked would also be useful in the end as a source for a post on blog.wikimedia.org, which seems appropriate for such an effort (there's time to think about it later). On CategoryTagSorter I asked a question on talk; on the process in general, please remember to document what are the obstacles you encounter in the process (which you may forget later) and what are the highest "costs" of the move when at full steam. Something like "30 % of the time for each extension is spent figuring out those crazy mediawiki.org templates"; it's fine on your own internal docs, to be shared with us later so that we can reduce attrition or tell others in the future.
Nemo