I think first and foremost, crowd control procs should be added to follower items, allowing you to get 4-5% on your amulet, 2handed weapon, and follower item might make for some unique variety and effectiveness. Also, in terms of Legendary follower items, simple things like wiz spike/storm crow/hellfire ring procs or other such effects to allow buffing/crowd control(burning axe of sankis - ignore pain, etc).
I agree with previous posts an interesting gem effect would be welcomed. I'm also one for allowing followers into group play. Way I see it is while we normally have a follower with us soloing(even if dps is negligable) with a flat increase to mob hp in parties, we could very well be less effective in a party because of the lack of followers while dealing with the same mob hp.
I'm also curious as to why with all of effort made towards 0 permenance gameplay the followers can't be respecced? Would gladly be corrected if I'm wrong on this one ;]