Would I? Yea ... I'm always inclined to use escape backticks in markdown actually. Basically anytime I'd be using or reading the relevant text in a programmatic/ASCII/monospace environment. I even use them to signify verbatim quotations. I find myself holding back on lemmy though because their styling can be a tad gaudy.

In the case of a unix path, yea I almost always would escape that with backticks. I do appreciate your angst at seeing the rendering of the path.

I'm not sure much of markdown is common knowledge apart from the basics. I think most people kinda fumble through the weirdness and idiosyncrasies of any particular flavour without caring too much about it in the end. But no, I don't think the specific replacements would be common knowledge. But I do think many would react pleasantly at most of them, in part because I don't think they're foreign in the text formatting space.

For me the main replacements I have a major problem with is reducing multiple question and exclamation points down to 3. That seems unnecessary to me. Though, to be clear, I'm not fond of the ellipsis substitution either. As for the rest, the only ones I like are the n-dash and m-dash substitutions and the quotation marks. The rest I'd classify as cute and unnecessary and the sort of thing that, if desirable, ought to be left to special syntax for special characters.

As for whether lemmy should use markdown-it ... I'm thinking it isn't a big issue and these replacements are just a particular flavour's idiosyncrasies that most are happy to deal with.

Two issues I'd raise though:

1. The lack of documentation about them in the lemmy docs on text formatting ... though either of us could probably be helping that with a PR rather than ranting here.
2. Getting the formatting of inline/block code less gaudy and more natural looking, so that using them feels less extreme.