Refinements proposed in Ruby 2.0 allows you to localise monkey-patching much like you can do in Perl with dynamic scoping (for e.g.: http://news.ycombinator.com/item?id=1603321 | http://news.ycombinator.com/item?id=3455507). For further info on Ruby refinements see here: http://timelessrepo.com/refinements-in-ruby

Traits are an improvement to mixins. IIRC Matz gave a talk (RubyConf 2010?) where he describes the proposed traits implementation. Here's one set of slides (not Matz's talk) which also shows some traits examples - http://www.slideshare.net/fabiokung/ruby-20-to-infinity-and-...