Aloha from Hawaii! 
I am a passionate Strava route creator and would love to see a private file system added to the “My Routes” feature of Strava web and mobile. It would simply all subfolders in “My Routes” and allow you to name and assign routes built to a folder for organization. It’s not like I have hundreds of routes (yet) but I’d love to group them by relatedness for ease of access. For a user story example: I am a trail runner here in Hawaii and there are a lot of undesignated trails that require me to build routes using manual mode. Route builder has all the tools I need to make a great route but for some particular mountains here, I make several routes that split one long trek into smaller routes for more reasonable efforts. There are about 8 total sections to this group of routes. As someone who builds plenty of bike, road, and trail routes I’d find it extremely efficient to be able to sort these routes into folders based on categories I privately label. If I ever leave Hawaii, I’d want to be able to drop all my subfolders of routes into a larger folder labeled “Hawaii Routes” so I don’t have to filter or scroll through them when I move somewhere new. I’m aware that there’s a filter feature, just putting this idea out there as well. Let me know people’s thoughts? And if it’s already been considered!