The instructions here, http://www.gentoo.org/proj/en/gentoo-alt/prefix/bootstrap-macos.xml, allow one to build a prefixed portage tree via subversion, but it's very incomplete. For example, under sci-biology there are 25 ebuilds, but on Linux, there are 65. Why are the others missing? Surely, a few here and there won't compile or be feasible, but why would so many summarily be excluded from portage?
simply put: because one man can't keep up with 300+ devs on the main tree. If you feel like helping out, patches etc. are much appreciated. Check out gentoo-alt mailing list, and contact the maintainer of prefix-users overlay if you want to share/try out your ebuilds with others because I import them in the tree, once I have a bit of time next to solving many bugs.
I don't really understand. How are the packages here different from the regular tree? They seem look the same. Is it just that only tested packages are being provided? But that doesn't seem to make sense because aren't the keywords/masking states to supposed to take care of what doesn't work?
have a look at http://www.gentoo.org/proj/en/gentoo-alt/prefix/techdocs.xml The net result is that each and every ebuild has to be manually checked and imported. Luckily there are some stupid helper scripts that tackle 90% of the cases, but keeping the prefix tree in sync with the main tree is a tedious job.