1. A clear explanation of a symbol system and how math is a symbol system to deal with issues of quantity, shape, structure, and logic.
2. Frequently converting between diagrams/drawings and symbols (show "x x x" at times and "3" at other times). I actually have a concept for a game I want to program that does this.
3. Showing multiple concrete applications of different ideas, and lots of word problems. In retrospect I think this was always reversed in the American system. We would learn the symbolic and algorithmic aspects of a math concept, then use it to solve some word problems. Once I went back and started teaching myself some of this stuff, I read that the Russian system is quite the opposite: lots of word problems, multi-faceted problems. I suspect I would have learned from that style a lot better.
EDIT: One more point I should make. I scored in the 85th percentile on my SAT math. It is probably not a great sign for our system of education that I could do so well with nothing but the most rudimentary understanding of what I was doing.
Interestingly, much of what you describe is present in old mathematical texts. For example, Fibonacci's Liber Abaci is essentially a long succession of story problems. Diophantus's Arithmetic is a succession of concrete problems -- no story -- but it's concrete prior to abstract as you suggest.
Euclid II also develops most of Algebra geometrically, so there's much conversion between shape and symbol baked it. His method of computing the product of binomials is far superior to what's commonly taught.
So there's a good tradition of the thing you're looking for!
I liked math in high school and usually saw the underlying meaning of the concepts. Teachers generally aren't idiots (or at least mine weren't), they try to explain it best they can, and start with that explanation. I remember explaining the meaning to friends that had only tried to memorize the rules without bothering to consider what they meant. They were surprised to learn these meaningful explanations, but in fact I was just repeating what the teacher had told us. I think the difference is I came into the class knowing what I should, while they had gaps in their prior teaching that they had to compensate for with memorization. So I was ready to hear the motivation at the start, but others weren't ready yet until they had memorized the concepts as a kind of crutch.
What you want is methodology like "just in time learning" or "problem based learning", which is very powerful but also very slow. You have to greatly reduce the content you can cover in a class. It's good for some students, boring for the smart ones (who solve your fancy word problems instantly), and the worst ones don't pay attention or do homework either way.
I'm not really convinced that's the case. As I mentioned, the Russian system is apparently very much like this, and they don't seem to have a problem producing large numbers of advanced quantitative thinkers. I also take a little exception to the implication that I wasn't one of the "smart ones." I had no problem doing what I was taught, I got good grades at at an advanced prep school, and I scored just fine on standardized tests. I basically succeeded according to every standard set by the system, and yet I wouldn't say I really learned very much. To me that signifies a real problem. I certainly deserve some of the blame, but definitely not all of it.
You're not convinced of what exactly? That alternative methods reduce content? That is precisely what you are instructed to do by pedagogy researchers giving advice to teachers.
Asian education systems like India, China, Japan are very rigid and based on rote practice and memorization. "Prep school" there means evening schools where they just go do yet more memorization and rote practice to help pass entrance exams. Yet they produce many brilliant mathematicians too. Of course the students are motivated by parents and society, not love of cramming.
The ideal would be teaching that is individualized and does the best it can to get through to each student (there are plenty of efforts and even "edTech" that tries to do this, especially at lower grades). Without that it's always a trade-off in which students get the most value for the time spent.
You said it's "boring for the smart ones," which I took to mean that if we go by the methodology I'm suggesting, we'll bore all the smart students, they'll have less knowledge, and we'll produce fewer good ones. Maybe you didn't mean all of that, but if you did, my point was that the Russian system, which seems to operate this way, seems to do just fine in keeping good students motivated and producing lots of talented mathematicians. I'm not convinced volume of content = engagement and better outcomes, either for "the smart ones" or the rest.
1. A clear explanation of a symbol system and how math is a symbol system to deal with issues of quantity, shape, structure, and logic.
2. Frequently converting between diagrams/drawings and symbols (show "x x x" at times and "3" at other times). I actually have a concept for a game I want to program that does this.
3. Showing multiple concrete applications of different ideas, and lots of word problems. In retrospect I think this was always reversed in the American system. We would learn the symbolic and algorithmic aspects of a math concept, then use it to solve some word problems. Once I went back and started teaching myself some of this stuff, I read that the Russian system is quite the opposite: lots of word problems, multi-faceted problems. I suspect I would have learned from that style a lot better.
EDIT: One more point I should make. I scored in the 85th percentile on my SAT math. It is probably not a great sign for our system of education that I could do so well with nothing but the most rudimentary understanding of what I was doing.