I have modified the ebuild for app-arch/tar to support -a / --lzma flags for using lzma-utils (more elegantly). This can be enabled with an lzma use flag. Reproducible: Always
Created attachment 142727 [details] tar-1.19-r2.ebuild the modified ebuild
Created attachment 142728 [details, diff] tar-1.19-use-lzma.patch patch required by the above ebuild
tar is a very old package ... mucking with its runtime options is not to be done without upstream going for it
tar-1.21 introduced lzma. we have tar-1.22 but still i don't have --lzma nor -J options!