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You can use this to win longer games by getting your two best permanent decks, and the other effect can disrupt the opponent or be used to shuffle your best cards back into your deck

My guess is that Amulet of Safekeeping is R&Ds attempt to try and answer the question of how to ensure that Modern players can sideboard against multiple strategies at once so that your progression though a large Modern tournament is less matchup dependent

Note that you do not target their creature, they choose it, so it plays like a Diabolic Edict effect where they send in their worst creature, rather than a better creature

With this in mind, it seems unlikely that Glorious End will show up in the main deck, but it could be a sideboard option for specific matchups (it's a hilariously effective way to win the mirror)