The last major update (MyM) contained several item rebalances that improved weapon balance in a competitive context and I believe the next major update will follow suit. By unbanning a few items this past season we have gathered some experience with more items which goes a long way towards giving our evaluations of the items any credibility in Valve's eyes. If these two trends continue, I think every weapon could reach a point where a banlist is not required, which would be huge for the approachability of competitive TF2. Even those first couple days where BASE Jumper and Atomizer were legal were an extremely valuable part of the whole global whitelist project so far because they gave us experience with those items. One of the big problems with testing anything in TF2 has been that people don't play normally/seriously when new factors are introduced, so having teams give them a fair shake was actually huge.
I don't think there is too much change that can be made to the global whitelist at this point, and I certainly don't feel that any of the items that are currently legal have proven to be game breaking or requiring a ban. It might have taken some adjusting to things like Rescue Ranger or Jarate, but they have become fairly inconsequential in the bigger picture of things. Now that we have this very small pool of banned items, the best thing to do from this point forward, besides waiting for the next major update to see how it affects current items, would be to systematically experiment with some of the unlocks that have either never been tested in a competitive setting, have recently been rebalanced but remain untested, or are considered borderline balanced. I think we should start with the Quick-Fix.