My husband built https://wikimap.wiki which shows every geotagged Wikipedia article on a map at once. It was actually quite complex to do this because of the large number of articles. The UI makes some compromises to try to keep it usable but it's a tough nut to crack with the highly variable density. It also has filtering by category and some features of that nature.
The major trick is that the article icons are a layer of prerendered tiles; the client can't handle that many objects. Clicking does a request to a geojson server backed by postgis to find what's in the region you clicked. I'm not sure that it's actually updating right now either, ingesting updates takes hours and is pretty brittle because of issues with the format of the dumps Wikipedia provides.
The major trick is that the article icons are a layer of prerendered tiles; the client can't handle that many objects. Clicking does a request to a geojson server backed by postgis to find what's in the region you clicked. I'm not sure that it's actually updating right now either, ingesting updates takes hours and is pretty brittle because of issues with the format of the dumps Wikipedia provides.