During the hackathon I will attempt to implement a template system which separates code, data, and layout, using Scribunto and the Parsoid DOM. More information on the rationale is listed at my talk description at https://wikimania2015.wikimedia.org/wiki/Submissions/Templates_are_dead!_Long_live_templates!
I'm definitely going to be working on this in connection with my talk presentation. I'd love to involve anyone else who wants to hack on it, or just talk about template engines and mediawiki content architecture.