If you need more typesetting control than what Markdown allows, dropping down to HTML is always an option.
To the second point, while it's possible that content could render differently if you change renderers, I would presume the folks at Mozilla are aware of this and won't do it unless it's absolutely necessary.
Do we actually know which renderer MDN is using? I don't see this mentioned in the post. I would argue that although alternate implementations exist, Gruber's `markdown.pl` is Markdown (whatever it does, warts and all) and deviating from it is generally a bad idea if you can avoid it.
Is it? In the public setting? HTML comes with things missing from Markdown that you want, sure, but it also comes with a full scripting environment, the ability to arbitrarily inject code and so on.
If you can drop to HTML, you have to have a sanitiser process. So then you're dropping to some-unknown-subset of HTML if the process is automatic - or you've failed to reduce the amount of effort being put on the editors if it's a human one.
For a place like MDN, this really isn't a problem.
> If you can drop to HTML, you have to have a sanitiser process. So then you're dropping to some-unknown-subset of HTML if the process is automatic - or you've failed to reduce the amount of effort being put on the editors if it's a human one.
I presume Kuma had - and Yari will have, if it doesn't already - some way to prevent unsafe injection and other dangerous things.
This isn't to say that the issue doesn't exist. Instead, I would expect it to be the exception rather than the rule. After all, Markdown and its derivatives owe their existence to this very phenomenon.
The language of last resort, if you will.
Other things that are critical features for development documentation, like tables, are extensions which may or may not completely break if you ever change your Markdown renderer.