I would add coffeescript-style instance variable setting to ruby method definitions like so:

  def initialize(foo, bar, baz)

    @foo=foo

    @bar=bar

    @baz=baz

  end

Would now be:

  def initialize(@foo, @bar, @baz)

  end

This would save hundreds of lines of code in large programs-- lines which could no longer be a source of typos or errors.

Oh, also I'd make binding_of_caller work.