I'm not able to develop a working solution for this but I think it should be possible. The extent indicator in the overview map is just a graphic so you should be able to modify it. Here's a solution that modifies a static graphic in a map view. I was also able to get the cursor to change when mousing over the overview extent graphic. You can use this on the 4.x example from above.
// get screenpoint from mapView's pointer-move event
mapView.on("pointer-move", function(event) {
mapView.hitTest(event, {include: mapView.graphics}).then(function(response) {
// check if a feature is returned from the hurricanesLayer
if (response.results.length) {
document.getElementById("overviewDiv").style.cursor = "move";
const graphic = response.results[0].graphic;
// do something with the graphic
} else {
document.getElementById("overviewDiv").style.cursor = "default";
}
});
});
Be sure to post back here if you're able to build a working solution! 😀