Really well thought out post. I can't believe it hasn't gotten any attention. I really find the topic of reading interesting for the reasons you say ("It’s extremely difficult to measure, fluctuates a lot and has various independent facets") and I've collected the opinions of various people on the forums and youtube.
My favorite part about this guide is that it verifies everything I've come to try and implement into my own gameplay. I heard rohulk talk about his way of reading the notes as they come up, similar to your idea of the "Goldilocks zone" or "queue". This idea makes a lot of sense to me, and when I implement it I feel like I'm playing "properly". I like to think of it as a conveyor belt myself. I've noticed that I feel the most in the zone when I'm reading in that way, but it also takes a lot of focus. Sometimes I want to look at the whole screen because I don't trust myself to be able to hit the pattern without trying to gather more data. However, this is usually counterproductive, because, as you pointed out, I'm trying to gather too much data and end up messing up in the processing or execution step as a result.
I also 100% agree that reading is a lot about focus. When I want to FC consistently, I feel like more than warming up my aim or streams, I just need to focus as much as possible, and that whether or not I FC is often a matter of if I kept my eyes looking at the right stuff. For example, when I start to panic because I'm FCing, I almost always start looking ahead because I "don't want to miss something" and end up moving too fast in execution. In other instances, I will just make my focus very broad. And if the map gets too easy I can lose proper focus and miss on something because I misread it and felt like I could just let my muscle memory do it.
I admit that I'm one of the people that thought AR8 improved reading. Your argument is that most AR8 maps tend to be too easy. However, I think for lower ranked players who are already playing some of the easier maps it can help. Wouldn't you agree?
I want to go into some questions and potential criticisms I have, but it's not to try and undermine what you say, but because I'm honestly curious and want to pick your brain for what you think.
The Model: I see why you made the model the way you did, and as they say all models are wrong but some are useful. And this is a very useful model. However, I feel like there is some overlap between the steps.
For example, if you overload yourself on information and you mess up, who is to say whether this mess up occured because of your processing or your plan or your execution? Wouldn't an execution mess up be a result of a previous step? Would an execution mess up by itself just be a mechanical error and thus not be related to reading? Overall, the model makes plenty of sense, but I don't fully understand this part.
Moving in a straight line and focusing on one circle:While I agree that this makes sense most of the time, I believe there are some patterns that most players can partially hit through muscle memory. I know because with certain things, like back and forths for example, your hand knows how to go back and forth between two spots without even looking. Of course this gets trickier the more complex the pattern becomes and the more likely you are to mess it up (like overlapping star pattern that's really close together and comes back in on itself). Of course it is probably almost always better to look, but I get the feeling that you learn an adaptable muscle memory for certain patterns. Even though no two patterns are exactly alike (with some exceptions), I feel like this muscle memory aids a lot in helping you hit things, and in some cases can even be leaned on as soon as you recognize the pattern.
My exhibit A for this is Cookiezi, who has said in his Happystick interview that at this point he just looks at the center of his screen and plays through periphery. Granted, he admits in the same breath that it is more consistent to actually look at the circles, but it's more fatiguing and makes him too tired, which goes along with what you said. Anyway, Cookie probably looked more at circles in the past and built up his reading that way, but the fact that he can play at such a high level now makes it seem like it's a totally viable way to play.
Pattern Recognition/Circle Configurations: One more thing with Cookiezi from this interview that reinforces my previous point is that Toy and Happy speculate that Cookiezi looks at osu! as a series of patterns in his head, and once he knows how to play a pattern he can (almost) always do it. Cookiezi also talks in this way. To paraphrase, he said something like "If you can't hit it you just aren't good enough, you can't expect to hit harder versions of a pattern if you can't hit easier ones".
Also, it's commonly accepted wisdom that playing many maps and exposing yourself to patterns makes it easier to play things you have never seen before. I personally think that pattern recognition is a big part of reading as well and it doesn't all come down to hitting what's in front of you. I think in the periphery you recognize patterns and prime yourself to hit them in your "queue". This also ties back into muscle memory, because although your hand hasn't done the same motions, it's certainly done similar ones and they will be easier the next time you do them.
However, this particular part doesn't really run counter to your model, but I think it could be integrated with it. Perhaps this could all be included in execution.
Sources:
Cookiezi Interview:
https://youtu.be/4-0rZ8YwGnERohulk Interview:
https://youtu.be/qDTdc4Onnw8