Remake Destiny 1 with the same content and features, but update the engine first, then add the new stuff from Destiny 2. No portal system.
But Destiny 1 wouldn't end like the old destiny 1 it would continue into destiny 2 until the end of Final Shape.
Update the features for a couple of years and release content, while you make the next destiny experience like a destiny 3.
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Bungie should just release d3 but it is actually a downgrade from the previous game and takes 4 years to be on par with its predecessor like they did last time.