The problem is, Vue.set is documented exactly nowhere in the getting started guide[0]. In my case, I couldn't use it because I wasn't the one modifying the data binder, d3-force was. But either way, this should definitely be in the guide !

Besides, it's possible for the new property to be picked up through Proxy Objects[1]. So it's not like it's entirely impossible for Vue to do this, they just chose not to (and they probably have good reason, like IE support).

[0]: https://vuejs.org/v2/guide/index.html

[1]: https://caniuse.com/#feat=proxy