I’m not a writer, I’m a technician. If I work with a computer, I edit documents in 10% of all cases at most, in 90% I look for information, read specifications, documentation and my notes. I take notes in markdown. And yes, a document written in markdown can be understood with a little effort, but if I want to interpret the content reliably, I need a preview of the document and I often need to quickly switch between multiple markdown documents. If I have to double click on each of my notes to open the document in an external editor (forget QuickLook, it has a lot of bugs, it doesn’t work), then my work is not efficient at all.
More than a year ago I wrote in this forum that I think a decent viewer would be enough, and for editing everyone can choose an editor according to their taste. Since even this minimal option is not available and the markdown format is obviously ignored in EagleFiler, I have switched to DevonThink, which supports markdown preview pretty well (after some CSS tweaking). For editing I use my favourite external editor. Pity, because otherwise I quite like EagleFiler.