I would argue that it is consistent now. At the lowest level, you have commonmark. Then, you have extensions at the top, such as GFM. If Pandoc/Github/Reddit/

I would argue that it is consistent now. At the lowest level, you have commonmark. Then, you have extensions at the top, such as GFM. If Pandoc/Github/Reddit/SO/kramdown switch, that accounts for almost all front- and back-end cases that I care about. And given that the first four were actively involved with commonmark, I would take as given that they will support commonmark or a superset of it.