Do you think so ?
Are there any particular structures that feel intuitively excluded ?
If a node is incapable of being multi-line
Multi-line paragraphs are easily represented as a sequence of lines (just as in Taskpaper, and in Markdown too)
I find, in practice, that parent ⇄ child and sibling ⇄ sibling connection are the basis of all text structures.
FWIW I’ve sketched a fairly general draft script for Bike → Markdown (including continuous paragraphs, nested bullets, quotes and code snippets etc etc) here:
Draft demos: Copy As Markdown & Save As Markdown - Bike - Hog Bay Software Support