Add the class exotic to the Pale Heart loot pool on completion of the legendary difficulty campaign; or, add a 'solo' instance of the Dual Destiny exotic mission.
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I propose Duel Destiny (Friendless Mode) where it's just a straight hallway with a chest at the end that has a solid roll inside, just to appease solo players. Bonus points if confetti and a banner saying "you tried your best" fall from the ceiling.