Unfortunately, I happen to think that generics (as implemented) have serious flaws. There are just too many weird behaviours and odd corner cases. Just look how big the FAQ is - a sure sign of serious problems. And they also look darn ugly too!
A forked version has been created on sourceforge with generics, but that is far from ideal, as Apache can't link to it (official policy) nor can it easily be kept in sync. However, it does show that the task is possible. Could the fork be brought back to Apache? Well possibly, but that gets bogged down in bureaucracy when the forkers don't have Apache commit priviledges. Even more so when the relevant Apache committer (me) isn't particularly motivated by the issue (generics).
Anyway, I'd like to ask anyone reading this a question or two - do you want a generics JDK1.5 version of commons-collections? Would you mind if parts of the API were changed to fix API design flaws (this would be a major release after all...)? Please comment here, or at Commons JIRA. You can also just vote for the change at JIRA.