The author of this JS library: https://instant.page/ Alexandre Dieulot, reached out to me stating that we should consider using it. Last time we considered doing any kind of proximity/hover-based prefetching, I believe we decided not to because our pages are riddled with links and some people point where they read. Which for someone with a metered connection, could turn out to be very expensive. The Save-Data exists, but it's unclear to us if users who would benefit from it know how to turn it on in their user agent. We don't want someone in a developing country to learn about it because they ended up having a huge internet access bill due to browsing Wikipedia articles using browser defaults.
We could consider, however, implementing the most conservative mode of that library, which is prefetching on link mousedown. Before we get into that, though, I think we should measure the rate of abandonment (mousedown but cursor moved out before it turns into a click), as well as the typical delay between mousedown and click. Adding a prefetch link to the DOM and the user agent acting on it aren't instantaneous things (the browser is only supposed to do it when completely idle, including other tabs), so there's a possibility that the preloading attempt wouldn't be worthwhile in a lot of the cases because the delay between mousedown and click would be too short.