Hi Reinhard. I don't know if skopeo works (and how) with the sjoerdsimons fork. Personally, I prefer using the upstream project (https://github.com/ostreedev/ostree-go) to minimize divergences and also due that is the code used and tested with skopeo.
But, through the pull request and the issue from Jul 27, 2017 in github, I can see the efforts of Sjoerd to work in the upstream project and the little response obtained, and then understand the fork. Due my little experience in this matters, I add Andrej who is currently working with golang-github-sjoerdsimons-ostree-go and if he think that the Sjoerd fork is a viable replacement we can use it, close this ITP and remove the golang-github-ostreedev-ostree-go to avoid future confusions. Regards, JMPC