Why would I use a typesetting engine to output an epub or html? They are //by definition not typeset//, but the user e.g. increases font size and rewraps.

Perhaps you would enjoy the rest of the tooling, that may be useful in scientific contexts or in books discussing programming languages. Or perhaps you would also want to publish in PDF, like for an actual print book.

What kind of issues did you expect to encounter in translating Typst documents to other languages?