I will say that Jason Snell’s hunt for the perfect iOS Markdown writing tool is a fools errand. I should know, I have been on this very same hunt for years. The difference is that I have realised that there is no single tool to rule them all. Rather what we are truly blessed with is a incredible ecosystem of applications with their very own strength.
I actually removed Simplenote from my setup and so my text is focused across Drafts (Micro.blog and now Twitter), iA Writer (long form writing) and my Zettelkasten. I do feel there is room for an Obsedian-like application for iOS that caters to the Zettelkasten crowd — 1Writer is great but could be soo much better, except development is seemingly very slow.