I developed NP_Indic, a Nucleus CMS plugin.
This plugin allows the user to post in Indic languages and use transliteration (or more specifically Romanization) while authoring the post.
This plugin uses popular WYSIWYG editor TinyMCE and GaMaBhaNa - a Javascript based Transliteration utility for Indic languages.
The plugin is built on top of existing NP_TinyMCE2 plugin.
The detailed installation instructions are maintained at Nuclues CMS Plugin Wiki.