I suspect that markdown or semi-complicated html (like you, I occasionally like to do this too, even if it's just bold or italics) in replies are a second class citizen because most major CMSes (including Known) strip out or severely limit (for security reasons) the html that is accepted in comment fields. In fact, to conserve on space, I've even noticed that many even strip out blank lines between paragraphs! Many also will mark as spam comments that have one or more URLs in them. As a result doing fancy or even mildly complicated html or markdown in replies is something for which most platforms just don't build.
The other issue in status updates and replies is that they're often syndicated to other platforms and it's a more difficult issue to properly do this with each snowflake social media silo depending on how they individually handle html/markdown (or not). I do this sometimes in WordPress to properly format syndicated content, and it easily triples the amount of manual work, so be careful what you wish for. (This may also be the reason I love Known so much too!)
Every now and then I'll write an extended reply to someone's post that gets to the point that headings, additional structure, and the frills become much more valuable. In those cases, I'd probably then default to make them posts/articles and add the additional touches and then do a manual mark up of u-in-reply-to to have them show up as a reply instead of just a mention. This happens so generally rarely that it's not too much of a headache.
Either way, the end result on the other person's site isn't something I can ever control for, so I try not to sweat it too much. :)
I’ve been reminded by Chris Aldrich of something I think I knew before: [M]ost major CMSes (including Known) strip out or severely limit (for security reasons) the html that is accepted in comment fields. … Many also will mark as spam comments that have one or more URLs in them. As a result doing fancy or even mildly complicated html or markdown in replies is something for which most platforms just don’t build. That’s fair enough. As ever, spammers are spoiling things for everyone. I do have an objection, though. If I am legitimately signed into my own site which, in the #indieweb, is where I will be if replying to some other site, then I’m unlikely to inject malicious code. And if I’m a spammer, and signed in under a false flag, then I’m not likely to need such subterfuges. A really helpful CMS would, surely, allow me to do all the formatting I want on something I am generating myself, regardless of the specific type of entry. Chris makes another point: The other issue in status updates and replies is that they’re often syndicated to other platforms and it’s a more difficult issue to properly do this with each snowflake social media silo depending on how they individually handle html/markdown (or not). Well, yes. But that’s not my problem on my site. Let them strip all they want, frankly, as long as the leave the link to my reply alone. As Chris acknowledges … Either way, the end result on the other person’s site isn’t something I can ever control for, so I try not to sweat it too much. :) For now, I think I’ll sweat this just a little, and add the u-in-reply-to by hand, and hope that does the needful.
Jeremy Cherfas, Jul 09 2017 on stream.jeremycherfas.net