Being first matters :')

I wrote a font for these, which does use the triangle-5 and the vertical layout: https://bobbiec.github.io/cistercian-font.html (recent discussion here: https://news.ycombinator.com/item?id=46939312)

And my associated writeup: https://digitalseams.com/blog/making-a-font-with-9999-ligatu... .

As mentioned in the blog, I think the horizontal layout makes more sense too (in terms of writing order). But just like the triangle-5, the vertical layout is more commonly seen, so that's what I stuck with.