It's nothing they have to worry about, really. All they would have to do is come up with a single word.
To be consistent with their namespace, it could be as simple as:
At least one stream shall exist at the following URL:
rtsp://my_camera_ip:554/onvif/device_services/default_stream
As for the implementation, no code would typically be necessary, only a configuration rule added to the RTSP server to issue an internal RTSP redirect to the propreitery URL.
You know how when you type in chrome SomeCompany.com you are really redirected SomeCompany.com/index.html or SomeCompany.com/main.cgi or SomeCompany.com/home.cfa?
Now imagine you had to know the "home.cfa" part when going to Wells Fargo but instead know to use "main.cgi" for moderncontractor.com...
That's what it's like with cameras.