Perhaps I don't understand Tonido correctly, but it seems to me that Tonido would scale just fine, it just pushes the scaling issues on to the user: "Can't access your photos? Make sure your Tonido server is up!"
If Tonido was a cloud computing solution, a large amount of demand would cause it either to magically launch a new Tonido Plug, or alternatively use the resources of someone else's unused Plug server.