There's nothing in the docs for repo2runnable that mentions appendable. MavenInstall could be made to handle appendable without much trouble.

My experience is that the vast majority of the time is spent in the p2 mirroring, so I don't think it's worth spending much effort on the much faster repo2runnable and mavenInstall phases. And it can always be done later :)

If it looks good to you, I'll merge this now. Oxygen.2 releases tomorrow, so I'll add support for that then cut a new release of Goomph which includes your improvement here and Oxygen.2.