I’m curious, what other metadata field do you want new lines in?
I can’t recall if users have requested multi-line values in other fields. I could easily imagine it for a list of maintainers or authors, or perhaps the ‘description’ could allow a couple of lines. It’s less important to me that there’s a compelling use-case than that the format is irregular and uncompromising to potential use-cases.
FWIW, both examples for Author and Maintainer seem to contain a newline in the Core Metadata document.