Obsidian transclusion allows for the embedding of Markdown files within a Markdown file.
But that will only display in Obsidian (or in other apps that support transclusion?).
A feature should exist to write the content of transcluded files out into files which call them.
The feature should support this operation on both an individual basis (ie incorporate transclusions within a single, open file) and all documents in a vault.
This principle, and the latter scenario in particular, are in-line with the principles “Notes for your grandchildren” and “future-proof format” as they would support non-reliance on Obsidian.