In Island Cycling's Free Course difficulty, the game openly challenges the player to pop all 20 balloons that are spread widely throughout the island in less than 30 minutes, and which are not displayed on the in-game map. Considered very difficult by most players to accomplish within those 30 minutes, I recall doing it in mere 22min in 2015 by starting on the grasspatch near the top of the volcano.

I therefore propose adding that as a category or level for speedruns.

I'm so sorry for not seeing your post until now... :( I've thought about this idea as well and will add this as a subcategory for Island Cycling.