CommonMark is not trivial to implement efficiently... and not all sites need as much functionality as CommonMark provides. So, would you prefer sites to invent

CommonMark is not trivial to implement efficiently... and not all sites need as much functionality as CommonMark provides. So, would you prefer sites to invent something completely weird and new each time, or use something more familiar that looks like a subset of markdown? Sure, it can be done better or worse, but I don't think the concept is wrong. But honestly, many comment systems only have italics, quotes, lists, urls and maybe code, bold text and images... most of which have been indicated in plain txt files for a long time in quite consistent ways, hardly Markdown's trademark markup.