Markdown support. This means being able to dump in an entire markdown document if someone really wanted to, and it be formatted using standard markdown (e.g common mark spec 2).
Adding support for bold, italic, link and lists in a similar but not quite the same way as standard markdown was not markdown support, it was just a step in that direction.
Markdown support should include:
Full support for h1 - h5 tags using the hashtag
Blockquotes
Code tags (with support for language specification)
Thematic breakes
Tables
plus all the standard, widely used items on the spec linked above