ilvl should not be based upon the gear's actual ilvl but some measure of "useful" stats to that class. It should count weapon damage, VIT, main DPS stat (STR/DEX/etc) and any appropriate secondary stats (for instance parry would not count for a non-tank class and piety does not count for DoW classes). In such a system, crafting gear would count the same as an empty slot for a DoW class.

Just healed a tank in Haukke wearing a mix of i70 to i90 on the left and wholly inappropriate gear on the right (crafting and mage accessories). Very squishy.