I think you guys are perhaps missing the point about maintaining line of sight. It has nothing to do with seeing the path your aircraft is taking directly but everything to do with what you are seeing around the craft. The purpose of maintaining line of sight is for the prevention of accidents with other air users thus you must be able to see left of the craft, right and behind. You should also be able to re-acquire the aircraft in an instant should you take your eyes off the craft eg looking at telemetry. The idea of being able to take your goggles off and instantly finding your aircraft is not particularly practical in reality. Having an observer is a very sensible thing. The only time I would say that an observer isnt needed for safety so much is FPV racing (and for that matter I dont see the need for maintaining line of sight for this although marshals required to keep people straying into the race track area).