> It would be a simple change to portage to rebuild all dependencies of a library when that library is updated I believe e.g. freebsd's portmaster takes a -r s

> It would be a simple change to portage to rebuild all dependencies of a library when that library is updated I believe e.g. freebsd's portmaster takes a -r switch to mean "rebuild this and all its dependents" (I presume you meant revdeps here), which gets you quite a long way.