Grade Specific Filter
When in the route builder, have some sort of filter option that highlights grades similar to a popularity heatmap. Have drop downs where you can highlight ranges like 5-10% or 10-15% grade, or whatever a logical increment would be, and just have those segments light up. Alternatively, just toggle an overly that puts a color gradient down signifying the steepness of all roads and trails within the viewing area. Good way to find places for speed work or hill repeats based on prescribed workout criteria.