Release schedule / How to manually load master branch in packer

There is the instance_metadata_tags feature that was merged in February. But there hasnt been a release since, so I cannot use it.
Is there a release cycle when the next release will be done?

If that is not possible, would it possible to load the current master into packer? If you can, can someone show me how to do that, because I have been unable to find documentation around that.

Thanks.