Since 4.8, there has been a node called “Editor Apply Splines” which allows you to apply a regular spline to a landscape. The limitation of this however, is that it can only be called in the editor, and will not work at run-time. And so, this request is for the ability to use “Apply Splines” in-game.
Also, this request could be expanded to pretty much include the ability to dynamically modify/create landscapes which is a somewhat big feature that UE4 currently lacks. It’s a pretty big feature that could benefit a lot of projects looking to have procedural terrain!