... from which you could choose the actual eqipped sets. This would allow for one Equipment Template for Power with all power weapons (stats) and one for Conditions or Support with all condition/support weapons (stats) and it would solve the weapon swapping issues with Legendary Weapons.
Basically Equipment Templates would have multiple weapon loadout variants. But I assume ArenaNet is more interested in selling us full Equipment Templates, even when those are merely used to store weapon set variants.
Just having 4 additional slots for a passive set would already go a long way. Assuming of course that moving legendary weapons between the active and the passive set would not remove their customization and upgrades.
When you remove a legendary weapon from an Equipment Template, it looses all customizing and upgrades (put into inventory). Re-equipping it with the same stats, look, and upgrades is a lot more fiddling than re-equpping an exotic or ascended weapon from the inventory.