Before posting this as an issue, I wanted to check if I'm not missing some obvious way to do this. I've checked the source of the timestep (Engine.ApplyFrameLimit and then Engine.Update) and it doesn't seem like there's a mechanism for it.
I realize games can potentially scale the timestep directly, but this wouldn't affect for example animation.
Another reason to bring it up here is to discuss what others think such a scale should look like. At least one other engine exposes their fixed time and normal frame times directly, and I can see value in having multiple layers of time scales (say UI and main game, but there are other use cases where different animations should be scaled differently). To start with just being able to set an Engine.TimeScale or something similar would be usful.