I have used Ruby on Rails extensively for multiple projects and would like to help with this Project Idea!
I think actionable errors are a great idea as it will expedite the debugging process.
We could even provide some sort of rake task which can automagically generate static error templates for production environments so that developers have a base page to work their errors on! The styling could be derived from their implemented stylesheets so that it would fit their webpages look and feel as well.