It would be awesome if we were able to get something in exchange for passage coins. Maybe even be able to exchange 10 or 15 for exotic shards or etheric light from Xur or be able to use them to buy gear outright from the Disciple of Osiris.
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You can get something in exchange for passage coins, they're called boons, you can buy them from brother Vance. Being able to buy gear with them would defeat the purpose of the trials