Dave Jones is the AGPGART maintainer for 2.5.x. He will be the maintainer for 2.4.x also, but will not take that role until 2.4.x has the 'new' GART style interface backported. You can look at his page at http://www.codemonkey.org.uk
to find out the latest status on his work. The only stuff that makes it to linux.kernel, as well as the kernel mailing list are committed patches and discussion, not so much works in progress.