Stick with the orthogonal projection. Your students are going to see that much more in courses before/after your course. And in literature in general. It is mildly disconcerting to see the alternate projection when so used to the standard one.
Note, that this argument applies even if the alternate projection is "better". And the same thing applies with the many other questions we have with people obsessed with changing notation or the like. Or on Wikipedia with changing English grammar, spelling, etc. to something they think makes more sense (but is non standard).
There are many areas you can still innovate and improve. One is cost, of course. But I would challenge you to push for quality composition (ZERO typos, grammar errors, etc.). It is frustrating to use even purchased texts that contain errors. And unfortunately, amateur texts tend to be even worse on average. Make it an objective to be four dot oh!
Another area is quality pedagogy. Many amateur texts suffer from poor explanation (for NEW LEARNERS, not math colleagues!), even worse than the norm in professional texts, which have issues also. They tend to read like the grad student or new faculty explaining things to himself, not to his audience (with awareness of new learner limitations). Same thing for exercises/answers/examples/hints. (Squared! Since "doing" is how we learn, not monograph explication.)
Furthermore, you should have a sophisticated knowledge from assessing several other books of ways to skin the cat. This doesn't mean you can never have a new idea. But it is important if you're going to do "one more attempt at an X text" that you have looked at more than one. In other words, not just trying the project from scratch, with no perspective, learning as you go.
And resist the temptation (probably prone by personality to proofy mathematicians, but not people-savvy educators) of wanting to convert the world back to Beta from VHS.