I think that there should be possibility to upload GPX by sending email with GPX files attached to email like gpx@openstreetmap.org… It would ease uploading files from few mobile devices… And shouldn’t be hard to program into existing OSM system 
I can only imagine how much spam that would get 
It wouldn’t be hard to make your own also, and by doing it this way the email address wouldn’t need to be made public, and it would upload under your own account etc.