The Balinese Wikipedia (ban.wikipedia) has some pages in Bali script, linked manually from the corresponding Latin script pages. However most users don't know how to write in Bali script and don't have the necessary tooling.

On Wikisource however we'd need to be able to transcribe old works in Bali script using their actual script, so it's useful to help users do that. http://palmleaf.org/ uses ICU transliteration data with some Node binding, see:
https://github.com/longnow/icu-transliterator-service
https://github.com/longnow/node-icu-transliterator
https://tools.wmflabs.org/icu-transliterate/

I don't see the mapping upstream though:
http://userguide.icu-project.org/transforms/general#TOC-Rule-Based-Transliterators
http://userguide.icu-project.org/transforms/general/rules
https://github.com/unicode-org/icu/tree/master/icu4c/source/data/translit

Instructions: https://www.mediawiki.org/wiki/Extension:UniversalLanguageSelector#Adding_support_for_a_new_key_mapping_(input_method)

Context: https://wikisource.org/w/index.php?title=Wikisource:Scriptorium&oldid=772812#Balinese_Wikisource