Sign if you would like bungie to add a mode that allowed you to create things in an open area. Like a racing map, boss rush, PvP map, or anything you can set your mind to.[spoiler]Maybe they could add this in a DLC and include the mode with a file share. The maps would not give you any loot or rep though.[/spoiler]
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We don't even have custom matches, this is probably lowest in their priority list.