I was really excited when I read your post. I've long looked for a good MarkDown -> PDF or RTF workflow, so I gave KeenWrite a quick try. At first glance I really thought I'd be exactly the user for this tool, but quickly realized that the discoverability of KeenWrite isn't nearly good enough.
Upon launch, I'm presented with three panes. I've got a MarkDown authoring interface and an output preview. Great. I drop in some markdown and it renders.
Then I have a "variables.yaml" pane open with three little controls, "Create", "Rename", and "Delete". Ok... I'm editing a YAML file. But it's a clunky nested node editor. People can edit a MarkDown file but you don't think it's faster to simply let people edit YAML in text?
So, I get it, I'm editing a YAML file that stores metadata about... SOMETHING about my document output. Except I don't have a single example of a variable. Not a single one. I have no idea what variables are available and exploring every single menu option tells me nothing. Help only provides a small about page with no link to the documentation.
So, I go to keenwrite.com and click documentation. It takes me to a single GitLab readme that talks about different command line launch options, and then finally how to begin to use metadata, but the options all revolve around creating an .Rmd file and using R or creating a "definitions.yaml" instead of a "variables.yaml" in a seperate editor.
This is the moment I realize there's no chance this tool is going to be useful for me.