Why release a beta if it's just an alpha? All the features isn't there. Why have this [temp] milestone? https://github.com/rails/rails/milestones/5.0.0%20%5Btemp%5D
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...