IIRC the monospace font itself would have the cursive characters as its "italic" typeface, then the terminal would just need to be sent the control characters for italic text (i.e. https://rubjo.github.io/victor-mono/)

Oh I see, so it's one font but two styles. That makes more sense (though to be honest I don't think I knew older terminals could do italics either)

It can be tricky to make it work in Vim + Tmux etc., but it can be done provided the font includes it as normal italic typefaces. I use Victor Mono and iirc it's available in two variants depending on whether you want normal italic font or cursive.

I've been using it for a while now, can't say it makes a big difference(both positive or negative), but it kind of looks nice which is the point in the end.

Wezterm can use separate fonts for each style like italic and bold

The script may be the italic glyphs for that font.