It would be helpful to pull in regular updates for MARC Authority records rather than manually having to check for updates to subject headings. For example - an author passes away, the current behavior is you need to edit the authority record. It would be beneficial to connect to the LOC database to look for updates automatically. Apis for the LOC https://www.loc.gov/apis/
LoC doesn't have an API for authorities (unless you consider downloading them one-by-one via z39.50 an API). For bulk authorities, you're looking at https://www.loc.gov/cds/products/marcDist.php where it costs $13,555 per year to get access to their FTP server with updates for both names and subjects (and you have to contact them to ask whether your plans for redistribution meet with their approval). Sounds more like something for a paid plugin and webservice run by a support provider with lots of US-based customers than something for Koha's core.