Julia, I finally got around to reading this article, and I really enjoyed it. Luckily, we were already doing many of the things you suggested! Your focus on "True North" and 12-18 month objectives is really helpful at driving the thinking toward more pragmatic prioritization.
How do you tactically construct roadmaps for quarters 4, 5 and 6? Typically, I only create plans for Q+1, Q+2, and Q+3 which have ~75%, ~50%, and ~25% confidence respectively. Q+4 and beyond are lumped into a single category with very loose prioritization. In my experience, putting those items on specific quarters raises more questions than it imprecisely answers.