I'm pleased to say that there is already a way for you to share your private routes with other selected users. If you go to your My Account page there is a tick box labelled "let people I'm following see my private routes" - tick this then you can share private routes with any other user you follow on the site (search for their name in the search box and visit their profile page to follow them).
Cloud services have this in their security setting and I think it would welcome more members and just make sharing routes easier!
In security settings the owner can allow specific people via email address to see their private routes! They could also choose what others can do with the routes, edit, read, etc.
limited access passwords can be emailed to their people so they can access the routes.
Here is an example by drop box if folders can be created they then can be assign with access privillages.
With encryption secruity
This allows more sensitive stuff to be shared like with facebook and that members can know their pictures and things they share remains secure. I don't mind paying to make this avaliable for this website! :)