Seeing these discussions on dual classes and I really miss how Guildwars 1 had real dual classes.
Here's a suggestion on how to implement GW2 Dual Classes using a lot of the existing functionality available in the game now. This would add so much customization and variation to the game. It could also possibly/probably break the game (but why not?)
1. Unlock dual classes (can be unlocked in xpac)
2. All classes granted ability to weapon swap during combat (10 second cooldown in combat)
3. Each weapon bar is assigned to a specific class or elite specialization. This selection will control class specific extra bars like attunement, tool belts, shroud, virtues etc. Weapon swapping out of that weapon removes the ability to use active/passives from that selection (i.e. a mechanist bar swapping to an elementalist bar will lose the jade mech)
4. Can use any weapon available to the main or secondary class. If both classes can use an equipped weapon, you have the option to select which class weapon skills will be assigned to that weapon (probably by right-clicking on the equipped weapon and selected one vs the other).
5. A 4th trait line is opened. Each trait line can be selected from the following:
1st trait line: selected from any base specialization of main class
2nd trait line: can be selected from base specialization of main or secondary class
3rd trait line: can be selected from base/elite specialization of main class
4th trait line: can be selected from any base/elite specialization of main or secondary class
6. Secondary class is locked to whatever the 4th trait line is assigned (either a base or elite specialization). i.e. it's therefore possible to be double same base class like Warrior/Warrior. It's also possible to have double (but different) elite specialization from the main class (like Scourge/Harbinger). The main class still would be based on whatever the 3rd trait line is set to.
7. Elite specializations on secondary class will also need to be unlocked using hero points but all base skills do not need to be unlocked. More hero points will need to be added to the game or some method of reassigning hero points.
8. Utility bar. Utility bar uses existing restrictions of slot 1 healing/ slot 5 elite but skills may be selected from either class
9. (Optional - this might be difficult to develop) Ascended skill added. The Ascended skill is created from each trait line. A new keybind and button is added at the end of the utility bar. The passive version of the Ascended skill enhances all the selected options selected in that trait line. An active form of the skill creates an effect based on the combination of selected traits in the trait line.