Someone already mentioned this, but I think the ideal solution is to simply allow us to use all of our kit irrespective of item level, once we reach the appropriate level to use it.

I don't mind having my level lowered so that my base stats meet the criteria of a person who would be roughly at the correct level of the content, but the idea of having to suddenly lose everything I worked hard for sort of jibs me the wrong way.

Obviously item level would need to possibly synch'd down even harder to compensate from the extra damage a full kit provides, but hey -- I'll take that evil if it means not having that awkward transition when you're doing end-game content, but you're constantly having to reinforce bad gameplay/rotation habits because of level synch.