I have updated tcl/tk to version 8.4.x (currently both ebuilds are masked in package.mask). Looking at your ebuild, I suspect, that it can stop working or block. Please test it with new tcl/tk, and fix it or close bug, if it works. For examples of tcl/tk version detection see /usr/lib/tclConfig.sh, net-analyzer/rrdtool or media-sound/waif
What makes you think that it will block/not work? If you already upgraded to tcl/tk 8.4 on your box, could you test the tkabber ebuild yourself, perhaps?
Fixed DEPEND.