It has been four months since the GSoC 2013 code submission. At that time the Lua-Factory Plugin was usable but yet with some issues to be dealt.
It was in the last two weeks that most of those issues were solved together with a few recommendations from Juan and Bastien and tonight it was merged upstream in Grilo-Plugins repository.
The documentation for implementing a Lua sources will come soon.
If you want to try it, you can always find some guidance in #grilo channel.
News from Brazil
It is Carnaval!