Currently hiera supports one `hiera.yaml` file hardcoded to be in the same location as `puppet.conf` (which is the `config` puppet directive.
Having separate `hiera.yaml`'s per puppet environment would go along with having separate `site.pp`'s, modules, etc. per environment.
This feature is released in Puppet 4.4 / PE 2016.1 - See the full documentation here: https://docs.puppet.com/puppet/latest/reference/lookup_quick.html
R.I.Pienaar has a blog series about it too: https://www.devco.net/archives/2016/03/13/the-puppet-4-lookup-function.php
PUP-4474 for the work on "data in modules" which also covers "data in environments". TL;DR - yes it will be possible to have hiera data per environment, as well as hiera data in a module, and all of that in combination with the existing global hiera.
Use this ticket to comment on use-cases if you like, as the
PUP-4474 and related tickets are about the implementation and thus are far more detailed/technical.