I believe the latest sets (fighter, rogue and barbarian) are intended to allow for the full set bonus by equipping identical weapons. Probably should get Mortis to confirm if this is so.
I am thinking it would be interesting to extend this to the Hexblade, BG, DD and Paladin sets to give them more flexibility, but would understand if these sets do not receive this treatment if it is deemed to be not desirable.
EDIT: Arcane set still showing up with bonus 1 tier lower than normal. DSM set works fine, but dual Sear's Anlace (one sorc, one unupgraded) allows me to get full set bonuses