I’m pretty sure you would say “kana” to refer to them. That’s what some online Japanese dictionaries use when a word usually is written without kanji (下さい – Vocabulary details – jpdb, https://jisho.org/word/下さい).
That’s true, but in Japanese katakana has a few special uses, one of them is writing loan words/foreign names. And considering that the English level is usually very basic, it is probably easier to read in katakana, rather than hard-to-pronounce words in English. But I feel like most people can at least read English (even if it’s hard), but pronunciation can be all over the place. So yeah, it’s the same problem with Russian, but here older people can’t read English at all, while younger people generally can’t talk/comprehend any non-beginner level English, they can still read, even if the pronunciation is wrong. And since Typst has so many consonants, they are very hard to hear, so usually people who try to say it, say something like Тайп (Typ/type) Тайпс (Typs). Which is unfortunate, but it’s what it’s. If it becomes mainstream, then it probably won’t be an issue.