My "scrum leader" (who we handled agile just fine without before) is constantly complaining about points or priorities shifting, to the point that he'll tell us to not put what we're actually working on on the board because it'll mess up the burndown chart.
One of the 4 values of agile is "responding to change over following a plan". He's parroted this to us before, and yet still doesn't seem to see the irony.
Do you mean admonitions? E.g. info, warning, etc? There's precedent for that in commonly-used open source implementations, e.g. obsidian.md (which uses the same syntax, and started before). What semantics does it break? It's designed to read well in plaintext and render nicely even if used in a renderer that doesn't support admonitions, e.g.
As opposed to other common markdownish implementations that use nonsensical plaintext which renders poorly in alternative renderers. Here's a discussion on the topic in the CommonMark forums.