Google has updated the plugin to 5.4.1.0, and removed 5.3.1.0 from their servers. A simple ebuild copy seems enough to get it working. Tested with firefox, and video is being shown.
+*google-talkplugin-5.4.1.0 (25 May 2014) + + 25 May 2014; Christoph Junghans <ottxor@gentoo.org> + +google-talkplugin-5.4.1.0.ebuild: + version bump (bug #511488) +