Code coloration wouldn't be that useful (if the snippets are that long they should probably go in a separate pastebin or a proper repository, reddit's comments do just fine without)

On the other hand backslash escaping (the lack of it and emphasis clusterfuck drives me nuts), block quotes, inline code/monospace and links I really miss.

Section titles, lists and tables would be nice as well, though not deal breakers.

Considering the maintainers have repeatedly refused to make any improvement to comment formatting in almost 10 years since HN was created, I'm not holding my breath though, it's obvious nobody cares about comment authorship and craft.

my netiquette says, more than about three lines of code should go in a pastebin anyway

Then in a few years when someone is reading old posts the links to old services are broken or the service is gone. If the code is central to the comment, why would you put it some place other than the comment? If it's not small enough you can collapse it inline and if it's so large that you don't want it with the comment then perhaps you should be rethinking what you are posting.

tldr; practicality and longevity should trump netiquette.

I agree and this was my original thought. For example Reddit, for most of its life, relied on imgurl for hosting images. Before the single place images constantly broke after services died. With imgurl being third party even it has led to broken images at times (though with significantly less frequency). Now reddit is doing their own.

Hacker News is very technical and code heavy. Seems to make sense to me that some may want to communicate / discuss code itself. I could even see it opening up more conversations like "this is my implementation of X; thoughts?" or "do this in any other language" challenges.

That's a very personal netiquette :-)