The subscription model only works when the people you are selling to use your app a lot and find it indispensable. This model works for things like professional tools, which is what Ulysses is, and things like Day One, that has recently gone subscription.
I wasn’t a dark mode person. When I was programming in Coda 2 on my Mac when I just started doing it, the UI was white. I showed someone a screenshot of it and they joked, "real programmers use dark editors."