Hello Andy, thanks for you your interesting in contributing to Rails, we’re very happy about that!
Regarding your questions:
I think this has been implemented by this commit: https://github.com/rails/rails/commit/455d710242f24f0cfff89f626164493276e0f3e9, so we have one man down ;).
I’d be willing to give a +1 on that, I’ve already had this requirement before and I think it’s rather common. Others might have a different opinion though, so it might be good to wait for a little bit more of feedback before starting. Or you can also give it a try (if you’re willing to) and come up with some working code in a pull request as a first iteration, and we can discuss from there (at least some rough idea about how the API would work, like adding a proc to counter cache or something like that?)
That’s it. Hope that helps, and see you soon in the contributors list