Hi, I'm the author of the pull request. The pull request got stuck due to an issue with dynamic injection of local variables into view templates. (Explained more in the Aaron Patterson's RailsConf keynote[1]). We were planning to solve this issue before (potentially) merging the feature.

At the moment, it looks like the issue is solvable, and I have code that seems to solve it but still needs some refinement before I can submit a pull request about it.

I don't know what the Rails core team is planning about the feature, but considering how complex the whole thing is and how much there's still left to do, I'd guess that it won't make it to 5.0.

[1]: https://www.youtube.com/watch?v=B3gYklsN9uc&feature=youtu.be...