You can clone with
It'd be nice to see amenity=townhall rendered and it is important enough that it should be included in the default map. (likely at a z17,z18 zoom).
It's an active tag, used 45,000+ times, and a relatively uncontroversial tag.
Not sure if I'll have time to get around to proposal a style for it in a pull req, but a note to self just in case.
If you need an icon for the node objects of it, you could use the one found in HDM-cartoCSS (the svg for the icon is within the _maki.svg)