From what I see in the curriculum we use for my children if we stay on track with the current trajectory they'll finish by grade 8 what is usually called Precalculus (USA terminology, includes solutions of algebraic equations, factoring techniques, graphing rational functions, basic matrix arithmetic, solutions of inequalities, basic linear programming, trigonometry, logs, exponentials, basic theory of functions). Hypothetically, this leaves 4 years of high school to learn mathematics beyond this foundation.
Question: which course sequence would you suggest for a high school student who is ready to take calculus in their first year of high school ?
Assume the children are home-taught with a parent who has a graduate education in mathematics for the convenience of your answer if you wish. More to the point, don't worry much about the plausibility of your answer to "real-world" school situations. In particular, set-aside worries about keeping all students on the same track and/or a lack of expertise in the instructors in your ideal school. The goal here is not to create mathematicians, but, to give mathematics a proper scholarly introduction. To borrow Frenkel's terminology, to show them artistry, not just fence painting.
In Why do we teach calculus in high school rather than a different math course? I made a comment which prompted the creation of this question.