It appears that a transclusion has to be the first thing on a line. If there is any space before {{transcluded file.md}} the transclusion won't be processed.
What I would like to do is create an outline with a list, drawing topic notes from markdown files. If the transclusion were indented to match the indentation of the placeholder, it would make a nicely formatted outline.
For instance:
- a dark and stormy night
{{dreadfulcliches.md}}
{{meteorology.md}}
- more songs about buildings and food
{{zappa.md}}
Ideally, this would create an outline with a main topic, a dark and stormy night, followed by indented notes from dreadfulcliches.md and meteology.md. The two separate transclusions would need to preserve the list layout.
Next would be a subtopic with its notes indented more.
The use case would be a Zettelkasten of Markdown notes. The outline would serve to organize notes into narrative order.
That would be pretty cool.