This is a great reason and thought, I love it. 
I got excited because I’m a fan of obsidian (the rock), but also because of Steven Universe. Obsidian is omnipresent in the show, and also excitingly climactic; of any of the names to take from SU, Obsidian would be the best fit for the writing app of my dreams: a tool that fused my desire for markdown, back linking, to-do item support, and easy publishing.
Obsidian (.md) seems closest to that than anything else I’ve found so far, so, I’m pretty stoked about the name even if it did have nothing to do with Steven Universe. 