I think a good solution (for Ruby) would to add something like that to a future Ruby version. These things do conflict with Ruby's core semantics a bit, but they do open the door to some intriguing styles -- as does this: https://github.com/intridea/hashie
I proposed a not-dissimilar idea on ruby-core recently. It got a little support, but was mostly ignored. It can be remarkably difficult to get meaningful changes adopted.
If ruby core shrinks and more of the standard libraries move to gems, it will be easier to just write this sort of thing as a gem and let the best ideas win out. The state_machine gem is a great example of the slow (but very solid) evolution of acts_as_state_machine into a highly useful general ruby library.
