The 7th most popular request in this year's Wishlist survey was a coordinate picker. The simplest version of this would just be an interface that displays maps.wikimedia.org, let's you click on it somewhere, and returns the coordinates you clicked on. Adding an interface for looking up addresses would require a 3rd party API, so I think we should defer that.
Note that Community Tech is only working on the top 5 proposals from this year's wishlist, so this wish will not be worked on by them.