This has been incorporated into a project to re-implement the user lists of Wikipedia:Wikipedians into a set of Categories. Feel free to help! Virtually all lists found listed as subsections of Wikipedia:Wikipedians should be eventually converted into Categories and their included links converted to the new system by tagging them in the appropriate new categories.
Userbox for New York City {{User New York City}} looks like this, and it automatically adds the user to this category:
 | This user lives in, or hails from, New York City. |