I’ve got ReRun added to Routes now. You have to use the Go button to get to its page, then there will be a new button with a ‘play’ icon that’ll slide a marker along the route.
That said… I’d like look into some kind of ‘scrubber’ interface.
I’m thinking something along the lines of Chris’ gradient/scrubbing demo, but it would need a secondary UI. You can’t be expected to drag/scrub over a route when you’re unsure where it goes. There needs to be another left → right visualization of the route (like an elevation display that’s previously been requested) that you’d be able to drag/scrub over to have the marker animated.