xNesku
I remember a while back the observer for NA was high Diamond. I'm not sure about EU, but KR has Master level spectators. If you're higher elo than you're going to naturally sense where the fights are going to take place. Also really minor details that can be super important to highlight for the viewers. The more game knowledge you have, the better you are as an observer.
While being high ranked is a plus, it's certainly not a pre-requisite to becoming a good observer.
You are right that game knowledge is important, but you can have good game knowledge without having the time or mechanics to reach a high rank in LoL, and I wouldn't want to discourage passionate and thoughtful gold players from thinking they can never become a good observer.
As a producer, what I look for in observers are: Do they work well with others? Can they communicate clearly and decisively in a live production environment? Are they able to consistently prioritize the right action to show? (teamfight vs gank). I don't think being highly ranked are pre-requisites for any of these skills.
That will get you 85% of the way, and then the additional 15% comes from practice and experience. Can you tell when a player is baiting for a fight? Watching that play out might be more interesting than what jungle camp is being taken (or maybe not!) Do we have time to show a long replay before another fight breaks out? That depends on game-state, when objectives are coming up, etc. How proficient are they at using the League Director tool, and imagining new angles to highlight action (without clipping terrain, exposing missing textures, etc.)?
What I'm trying to say is, observing LoL is a pretty involved and one of the most important jobs on the live broadcast, but you don't need to be highly ranked to do a good job. If you're passion is to become a LoL observer, don't think you need to be diamond ranked to land an interview! If you can showcase some of the skills above, you'll go far.