FWIW, it’s likely that the absence of a text-centering plugin is deliberate (to the extent that a community/cultural consensus can be “deliberate”). After all, Markdown is a tool for structuring text, not styling it. (To put it another way, Markdown is a markup syntax for converting text to HTML, not to HTML+CSS!)
Empirically, we should not expect to find any centering plugins any more than we should expect to find Markdown plugins to paint your text with all the colors of the rainbow, to change the font to Zapfino, to rotate it 75° counterclockwise, etc.; and, normatively, we should not write such plugins (even though we totally could).
FWIW, it’s likely that the absence of a text-centering plugin is deliberate (to the extent that a community/cultural consensus can be “deliberate”). After all, Markdown is a tool for structuring text, not styling it. (To put it another way, Markdown is a markup syntax for converting text to HTML, not to HTML+CSS!)
Empirically, we should not expect to find any centering plugins any more than we should expect to find Markdown plugins to paint your text with all the colors of the rainbow, to change the font to Zapfino, to rotate it 75° counterclockwise, etc.; and, normatively, we should not write such plugins (even though we totally could).