I doubt it's possible. Gentoo packages have two major characteristics, the keywords (that define stable or testing branch) and the USE flags (that add/disable features). Assuming in the future the r10k gentoo package has USE flags, we will need extra code in the future to separate which of the `provider_options` are USE flags or keywords. In case of more providers this adds even more complexity. I realized though that I don't have a default (empty) variable for this in `r10k::params`, is that a problem?