Nah, you really want to start students learning the GA formalism in their linear algebra and vector calculus classes, if not in high school.

Especially important in high school is to dive into not only the “complex numbers” but also the “split complex numbers”.

Sure, as long as you don't expect anyone to complete the course or are willing to play catch up for most of the semester. In other words, I'd love to plan courses that way, but no university administrator would ever let me (instead I restrict myself to graduate seminars and beyond).