Following the recent SourceForge account takeover and installer malware controversy, G'MIC's source tarballs are no longer hosted on SourceForge. Gentoo should provide a gimp-gmic-1.6.3.1 ebuild ASAP, and I will provide a URL for the tarball soon.
Tarball: http://gmic.eu/files/
Current stable version is now 1.6.5.0. It would be great to see this version entering the tree.
1.6.5.0 added to the tree.
Thank you!