Given the following example:

module SomeNamespace
  class Foo
    include Mongoid::Document
    recursively_embeds_many
  end
end

The methods it generates are literally:
"parent_some_namespace/foo"
"child_some_namespace/foos"

Might be nice to just have it use underscores all the way so that it can be a valid ruby method.

Workaround:
A temporary workaround for this as pointed out by Durran is to just create the embeds_many and embedded_in relationship like normal, but provide a ":cyclic => true" option to both of them.