Datto on Twitter stated that all upgraded and new exotics will start with a base damage of 300~. The only thing that you will really be missing out on are the unique perks. This makes a lot more sense regarding the decisions you must make when choosing to reset an exotic. EDIT: Datto also mentioned in his most previous stream that fellow Destiny streamer, "KingGothalion", spoke with Bungie employees about the exotic reset. They said to him, apparently, that it will take less XP to level new exotics