I know the norm currently is are set bonuses up to 5 PC's. This results in a popular mix and match of two 5 pc sets, etc. I'm not very happy with the results of people wearing two full 5 pc proc sets in PvP currently and it got me to thinking about set bonuses beyond 5.
I would love for a new DLC to add a new armor set (possibly 9 trait needed to craft) with set bonus' up to 8 traits. Those upper traits would have to be strong to counter the loss of the other pieces you might mix with them. Could be interesting.